Base station, and buffer partitioning method

ABSTRACT

Disclosed is a base station which transmits and retransmits to a terminal first and second downlink data in first and second component carriers, respectively, wherein a first configuration pattern of UL (uplink) and DL (downlink) subframes is set for the first component carrier and a second configuration pattern of UL and DL subframes is set for the second component carrier. The base station receives from the terminal in the first component carrier an ACK/NACK for the first and second downlink data received by the terminal, which stores retransmission data of the first and second downlink data in a soft buffer, wherein the soft buffer for the second downlink data is sized according to a maximum number of downlink HARQ retransmission processes executable in a reference configuration pattern of UL and DL subframes, and the reference configuration pattern is determined according to the first and second configuration patterns.

BACKGROUND Technical Field

The present invention relates to a terminal apparatus and a bufferdividing method.

Description of the Related Art

3GPP LTE employs Orthogonal Frequency Division Multiple Access (OFDMA)as a downlink communication scheme. In radio communication systems towhich 3GPP LTE is applied, base stations transmit synchronizationsignals (i.e., Synchronization Channel: SCH) and broadcast signals(i.e., Broadcast Channel: BCH) using predetermined communicationresources. Meanwhile, each terminal finds an SCH first and therebyensures synchronization with the base station. Subsequently, theterminal reads BCH information to acquire base station-specificparameters (e.g., frequency bandwidth) (see, Non-Patent Literature(hereinafter, abbreviated as NPL) 1, 2 and 3).

In addition, upon completion of the acquisition of the basestation-specific parameters, each terminal sends a connection request tothe base station to thereby establish a communication link with the basestation. The base station transmits control information via PhysicalDownlink Control CHannel (PDCCH) as appropriate to the terminal withwhich a communication link has been established via a downlink controlchannel or the like.

The terminal performs “blind-determination” on each of a plurality ofpieces of control information included in the received PDCCH signal(i.e., Downlink (DL) Assignment Control Information: also referred to asDownlink Control Information (DCI)).

To put it more specifically, each piece of the control informationincludes a Cyclic Redundancy Check (CRC) part and the base station masksthis CRC part using the terminal ID of the transmission target terminal.Accordingly, until the terminal demasks the CRC part of the receivedpiece of control information with its own terminal ID, the terminalcannot determine whether or not the piece of control information isintended for the terminal. In this blind-determination, if the result ofdemasking the CRC part indicates that the CRC operation is OK, the pieceof control information is determined as being intended for the terminal.

Moreover, in 3GPP LTE, Automatic Repeat Request (ARQ) is applied todownlink data to terminals from a base station. To put it morespecifically, each terminal feeds back a response signal indicating theresult of error detection on the downlink data to the base station. Eachterminal performs a CRC on the downlink data and feeds backAcknowledgment (ACK) when CRC=OK (no error) or Negative Acknowledgment(NACK) when CRC=Not OK (error) to the base station as a response signal.An uplink control channel such as Physical Uplink Control Channel(PUCCH) is used to feed back the response signals (i.e., ACK/NACKsignals (hereinafter, may be referred to as “A/N,” simply)).

The control information to be transmitted from a base station hereinincludes resource assignment information including information onresources assigned to the terminal by the base station. As describedabove, PDCCH is used to transmit this control information. This PDCCHincludes one or more L1/L2 control channels (L1/L2 CCH). Each L1/L2 CCHconsists of one or more Control Channel Elements (CCE). To put it morespecifically, a CCE is the basic unit used to map the controlinformation to PDCCH. Moreover, when a single L1/L2 CCH consists of aplurality of CCEs (2, 4 or 8), a plurality of contiguous CCEs startingfrom a CCE having an even index are assigned to the L1/L2 CCH. The basestation assigns the L1/L2 CCH to the resource assignment target terminalin accordance with the number of CCEs required for indicating thecontrol information to the resource assignment target terminal. The basestation maps the control information to physical resources correspondingto the CCEs of the L1/L2 CCH and transmits the mapped controlinformation.

In addition, CCEs are associated with component resources of PUCCH(hereinafter, may be referred to as “PUCCH resource”) in a one-to-onecorrespondence. Accordingly, a terminal that has received an L1/L2 CCHidentifies the component resources of PUCCH that correspond to the CCEsforming the L1/L2 CCH and transmits a response signal to the basestation using the identified resources. However, when the L1/L2 CCHoccupies a plurality of contiguous CCEs, the terminal transmits theresponse signal to the base station using a PUCCH component resourcecorresponding to a CCE having a smallest index among the plurality ofPUCCH component resources respectively corresponding to the plurality ofCCEs (i.e., PUCCH component resource associated with a CCE having aneven numbered CCE index). In this manner, the downlink communicationresources are efficiently used.

As illustrated in FIG. 1, a plurality of response signals transmittedfrom a plurality of terminals are spread using a Zero Auto-correlation(ZAC) sequence having the characteristic of zero autocorrelation intime-domain, a Walsh sequence and a discrete Fourier transform (DFT)sequence, and are code-multiplexed in a PUCCH. In FIG. 1, (W₀, W₁, W₂,W₃) represent a length-4 Walsh sequence and (F₀, F₁, F₂) represent alength-3 DFT sequence. As illustrated in FIG. 1, ACK or NACK responsesignals are primary-spread over frequency components corresponding to 1SC-FDMA symbol by a ZAC sequence (length-12) in frequency-domain. To putit more specifically, the length-12 ZAC sequence is multiplied by aresponse signal component represented by a complex number. Subsequently,the ZAC sequence serving as the response signals and reference signalsafter the primary-spread is secondary-spread in association with each ofa Walsh sequence (length-4: W₀-W₃ (may be referred to as Walsh CodeSequence)) and a DFT sequence (length-3: F₀-F₂). To put it morespecifically, each component of the signals of length-12 (i.e., responsesignals after primary-spread or ZAC sequence serving as referencesignals (i.e., Reference Signal Sequence) is multiplied by eachcomponent of an orthogonal code sequence (i.e., orthogonal sequence:Walsh sequence or DFT sequence). Moreover, the secondary-spread signalsare transformed into signals of length-12 in the time-domain by inversefast Fourier transform (IFFT). A CP is added to each signal obtained byIFFT processing, and the signals of one slot consisting of seven SC-FDMAsymbols are thus formed.

The response signals from different terminals are spread using ZACsequences each corresponding to a different cyclic shift value (i.e.,index) or orthogonal code sequences each corresponding to a differentsequence number (i.e., orthogonal cover index (OC index)). An orthogonalcode sequence is a combination of a Walsh sequence and a DFT sequence.In addition, an orthogonal code sequence is referred to as a block-wisespreading code in some cases. Thus, base stations can demultiplex thecode-multiplexed plurality of response signals using the related artdespreading and correlation processing (see, NPL 4).

However, it is not necessarily true that each terminal succeeds inreceiving downlink assignment control signals because the terminalperforms blind-determination in each subframe to find downlinkassignment control signals intended for the terminal. When the terminalfails to receive the downlink assignment control signals intended forthe terminal on a certain downlink component carrier, the terminal wouldnot even know whether or not there is downlink data intended for theterminal on the downlink component carrier. Accordingly, when a terminalfails to receive the downlink assignment control signals intended forthe terminal on a certain downlink component carrier, the terminalgenerates no response signals for the downlink data on the downlinkcomponent carrier. This error case is defined as discontinuoustransmission of ACK/NACK signals (DTX of response signals) in the sensethat the terminal transmits no response signals.

In 3GPP LTE systems (may be referred to as “LTE system,” hereinafter),base stations assign resources to uplink data and downlink data,independently. For this reason, in the 3GPP LTE system, terminals (i.e.,terminals compliant with LTE system (hereinafter, referred to as “LTEterminal”)) encounter a situation where the terminals need to transmituplink data and response signals for downlink data simultaneously in theuplink. In this situation, the response signals and uplink data from theterminals are transmitted using time-division multiplexing (TDM). Asdescribed above, the single carrier properties of transmission waveformsof the terminals are maintained by the simultaneous transmission ofresponse signals and uplink data using TDM.

In addition, as illustrated in FIG. 2, the response signals (i.e.,“A/N”) transmitted from each terminal partially occupy the resourcesassigned to uplink data (i.e., Physical Uplink Shared CHannel (PUSCH)resources) (i.e., response signals occupy some SC-FDMA symbols adjacentto SC-FDMA symbols to which reference signals (RS) are mapped) and arethereby transmitted to a base station in time-division multiplexing(TDM). However, “subcarriers” in the vertical axis in FIG. 2 are alsotermed as “virtual subcarriers” or “time contiguous signals,” and “timecontiguous signals” that are collectively inputted to a discrete Fouriertransform (DFT) circuit in a SC-FDMA transmitter are represented as“subcarriers” for convenience. To put it more specifically, optionaldata of the uplink data is punctured due to the response signals in thePUSCH resources. Accordingly, the quality of uplink data (e.g., codinggain) is significantly reduced due to the punctured bits of the codeduplink data. For this reason, base stations instruct the terminals touse a very low coding rate and/or to use very large transmission powerso as to compensate for the reduced quality of the uplink data due tothe puncturing.

Meanwhile, the standardization of 3GPP LTE-Advanced for realizing fastercommunication than 3GPP LTE is in progress. 3GPP LTE-Advanced systems(may be referred to as “LTE-A system,” hereinafter) follow LTE systems.3GPP LTE-Advanced will introduce base stations and terminals capable ofcommunicating with each other using a wideband frequency of 40 MHz orgreater to realize a downlink transmission rate of up to 1 Gbps orabove.

In the LTE-A system, in order to simultaneously achieve backwardcompatibility with the LTE system and ultra-high-speed communicationseveral times faster than transmission rates in the LTE system, theLTE-A system band is divided into “component carriers” of 20 MHz orbelow, which is the bandwidth supported by the LTE system. In otherwords, the “component carrier” is defined herein as a band having amaximum width of 20 MHz and as the basic unit of communication band. Inthe Frequency Division Duplex (FDD) system, moreover, “componentcarrier” in downlink (hereinafter, referred to as “downlink componentcarrier”) is defined as a band obtained by dividing a band according todownlink frequency bandwidth information in a BCH broadcasted from abase station or as a band defined by a distribution width when adownlink control channel (PDCCH) is distributed in the frequency domain.In addition, “component carrier” in uplink (hereinafter, referred to as“uplink component carrier”) may be defined as a band obtained bydividing a band according to uplink frequency band information in a BCHbroadcasted from a base station or as the basic unit of a communicationband of 20 MHz or below including a Physical Uplink Shared CHannel(PUSCH) in the vicinity of the center of the bandwidth and PUCCHs forLTE on both ends of the band. In addition, the term “component carrier”may be also referred to as “cell” in English in 3GPP LTE-Advanced.Furthermore, “component carrier” may also be abbreviated as CC(s).

In the Time Division Duplex (TDD) system, a downlink component carrierand an uplink component carrier have the same frequency band, anddownlink communication and uplink communication are realized byswitching between the downlink and uplink on a time division basis. Forthis reason, in the case of the TDD system, the downlink componentcarrier can also be expressed as “downlink communication timing in acomponent carrier.” The uplink component carrier can also be expressedas “uplink communication timing in a component carrier.” The downlinkcomponent carrier and the uplink component carrier are switched based ona UL-DL configuration as shown in FIG. 3.

In the UL-DL configuration shown in FIG. 3, timings are configured insubframe units (that is, 1 msec units) for downlink communication (DL)and uplink communication (UL) per frame (10 msec). The UL-DLconfiguration can construct a communication system capable of flexiblymeeting a downlink communication throughput requirement and an uplinkcommunication throughput requirement by changing a subframe ratiobetween downlink communication and uplink communication. For example,FIG. 3 illustrates UL-DL configurations (Config 0 to 6) having differentsubframe ratios between downlink communication and uplink communication.In addition, in FIG. 3, a downlink communication subframe is representedby “D,” an uplink communication subframe is represented by “U” and aspecial subframe is represented by “S.” Here, the special subframe is asubframe at the time of switchover from a downlink communicationsubframe to an uplink communication subframe. In the special subframe,downlink data communication may be performed as in the case of thedownlink communication subframe.

In each UL-DL configuration shown in FIG. 3, subframes (20 subframes)corresponding to 2 frames are expressed in two stages: subframes (“D”and “S” in the upper row) used for downlink communication and subframes(“U” in the lower row) used for uplink communication. Furthermore, asshown in FIG. 3, an error detection result corresponding to downlinkdata (ACK/NACK) is indicated in the fourth uplink communication subframeor an uplink communication subframe after the fourth subframe after thesubframe to which the downlink data is assigned.

The LTE-A system supports communication using a band obtained bybundling some component carriers, so-called carrier aggregation (CA).Note that while a UL-DL configuration can be set for each componentcarrier, an LTE-A system compliant terminal (hereinafter, referred to as“LTE-A terminal”) is designed assuming that the same UL-DL configurationis set among a plurality of component carriers.

FIGS. 4A and 4B are diagrams provided for describing asymmetric carrieraggregation and a control sequence thereof applicable to individualterminals.

As illustrated in FIG. 4B, a configuration in which carrier aggregationis performed using two downlink component carriers and one uplinkcomponent carrier on the left is set for terminal 1, while aconfiguration in which the two downlink component carriers identicalwith those used by terminal 1 are used but uplink component carrier onthe right is used for uplink communication is set for terminal 2.

Referring to terminal 1, a base station included in an LTE-A system(that is, LTE-A system compliant base station (hereinafter, referred toas “LTE-A base station”) and an LTE-A terminal included in the LTE-Asystem transmit and receive signals to and from each other in accordancewith the sequence diagram illustrated in FIG. 4A. As illustrated in FIG.4A, (1) terminal 1 is synchronized with the downlink component carrieron the left when starting communications with the base station and readsinformation on the uplink component carrier paired with the downlinkcomponent carrier on the left from a broadcast signal called systeminformation block type 1 (SIB1). (2) Using this uplink componentcarrier, terminal 1 starts communication with the base station bytransmitting, for example, a connection request to the base station. (3)When determining that a plurality of downlink component carriers need tobe assigned to the terminal, the base station instructs the terminal toadd a downlink component carrier. However, in this case, the number ofuplink component carriers does not increase, and terminal 1, which is anindividual terminal, starts asymmetric carrier aggregation.

In addition, in the LTE-A system to which carrier aggregation isapplied, a terminal may receive a plurality of pieces of downlink dataon a plurality of downlink component carriers at a time. In LTE-A,channel selection (also referred to as “multiplexing”), bundling and adiscrete Fourier transform spread orthogonal frequency divisionmultiplexing (DFT-S-OFDM) format are available as a method oftransmitting a plurality of response signals for the plurality of piecesof downlink data. In channel selection, a terminal causes not onlysymbol points used for response signals, but also the resources to whichthe response signals are mapped to vary in accordance with the patternfor results of the error detection on the plurality of pieces ofdownlink data. Compared with channel selection, in bundling, theterminal bundles ACK or NACK signals generated according to the resultsof error detection on the plurality of pieces of downlink data (i.e., bycalculating a logical AND of the results of error detection on theplurality of pieces of downlink data, provided that ACK=1 and NACK=0),and response signals are transmitted using one predetermine resource. Intransmission using the DFT-S-OFDM format, a terminal jointly encodes(i.e., joint coding) the response signals for the plurality of pieces ofdownlink data and transmits the coded data using the format (see, NPL5). For example, a terminal may feed back the response signals (i.e.,ACK/NACK) using channel selection, bundling or DFT-S-OFDM according tothe number of bits for a pattern for results of error detection.Alternatively, a base station may previously configure the method oftransmitting the response signals.

Channel Selection is a technique that varies not only the phase points(i.e., constellation points) for the response signals but also theresources used for transmission of the response signals (may be referredto as “PUCCH resource,” hereinafter) on the basis of whether the resultsof error detection on the plurality of pieces of downlink data for eachdownlink component carrier received on the plurality of downlinkcomponent carriers (a maximum of two downlink component carriers) areeach an ACK or NACK as illustrated in FIG. 5. Meanwhile, bundling is atechnique that bundles ACK/NACK signals for the plurality of pieces ofdownlink data into a single set of signals and thereby transmits thebundled signals using one predetermined resource (see, NPLs 6 and 7).Hereinafter, the set of the signals formed by bundling ACK/NACK signalsfor a plurality of pieces of downlink data into a single set of signalsmay be referred to as “bundled ACK/NACK signals.”

The following two methods are considered as a possible method oftransmitting response signals in uplink when a terminal receivesdownlink assignment control information via a PDCCH and receivesdownlink data.

One of the methods is to transmit response signals using a PUCCHresource associated in a one-to-one correspondence with a controlchannel element (CCE) occupied by the PDCCH (i.e., implicit signaling)(hereinafter, method 1). More specifically, when DCI intended for aterminal served by a base station is mapped in a PDCCH region, eachPDCCH occupies a resource consisting of one or a plurality of contiguousCCEs. In addition, as the number of CCEs occupied by a PDCCH (i.e., thenumber of aggregated CCEs: CCE aggregation level), one of aggregationlevels 1, 2, 4 and 8 is selected according to the number of informationbits of the assignment control information or a propagation pathcondition of the terminal, for example.

The other method is to previously indicate a PUCCH resource to eachterminal from a base station (i.e., explicit signaling) (hereinafter,method 2). To put it differently, each terminal transmits responsesignals using the PUCCH resource previously indicated by the basestation in method 2.

Furthermore, as shown in FIG. 5, the terminal transmits response signalsusing one of two component carriers. A component carrier that transmitssuch response signals is called “primary component carrier (PCC) orprimary cell (PCell).” The other component carrier is called “secondarycomponent carrier (SCC) or secondary cell (SCell).” For example, the PCC(PCell) is a component carrier that transmits broadcast information on acomponent carrier that transmits response signals (e.g., systeminformation block type 1 (SIB1)).

In method 2, PUCCH resources common to a plurality of terminals (e.g.,four PUCCH resources) may be previously indicated to the terminals froma base station. For example, terminals may employ a method to select onePUCCH resource to be actually used, on the basis of a transmit powercontrol (TPC) command of two bits included in DCI in SCell. In thiscase, the TPC command is also called an ACK/NACK resource indicator(ARI). Such a TPC command allows a certain terminal to use an explicitlysignaled PUCCH resource in a certain subframe while allowing anotherterminal to use the same explicitly signaled PUCCH resource in anothersubframe in the case of explicit signaling.

Meanwhile, in channel selection, a PUCCH resource in an uplink componentcarrier associated in a one-to-one correspondence with the top CCE indexof the CCEs occupied by the PDCCH indicating the PDSCH in PCC (PCell)(i.e., PUCCH resource in PUCCH region 1 in FIG. 5) is assigned (implicitsignaling).

Here, ARQ control using channel selection when the above asymmetriccarrier aggregation is applied to a terminal will be described withreference to FIG. 5 and FIGS. 6A and 6B.

For example, in FIG. 5, a component carrier group (may be referred to as“component carrier set” in English) consisting of component carrier 1(PCell) and component carrier 2 (SCell) is set for terminal 1. In thiscase, after downlink resource assignment information is transmitted toterminal 1 from the base station via a PDCCH of each of componentcarriers 1 and 2, downlink data is transmitted using the resourcecorresponding to the downlink resource assignment information.

Furthermore, in channel selection, response signals representing errordetection results corresponding to a plurality of pieces of downlinkdata in component carrier 1 (PCell) and error detection resultscorresponding to a plurality of pieces of downlink data in componentcarrier 2 (SCell) are mapped to PUCCH resources included in PUCCH region1 or PUCCH region 2. The terminal uses two types of phase points (BinaryPhase Shift Keying (BPSK) mapping) or four types of phase points(Quadrature Phase Shift Keying (QPSK) mapping) as response signalsthereof. That is, in channel selection, it is possible to express apattern for results of error detection corresponding to a plurality ofpieces of downlink data in component carrier 1 (PCell) and the resultsof error detection corresponding to a plurality of pieces of downlinkdata in component carrier 2 (SCell) by a combination of PUCCH resourcesand phase points.

Here, FIG. 6A shows a method of mapping a pattern for results of errordetection when the number of component carriers is two (one PCell, oneSCell) in a TDD system.

Note that FIG. 6A assumes a case where the transmission mode is set toone of (a), (b) and (c) below.

(a) A transmission mode in which each component carrier supports onlyone-CW (codeword) downlink transmission.

(b) A transmission mode in which one component carrier supports onlyone-CW downlink transmission and the other component carrier supports upto two-CW downlink transmission.

(c) A transmission mode in which each component carrier supports up totwo-CW downlink transmission.

Furthermore, FIG. 6A assumes a case where number M is set in one of (1)to (4) below, M indicating how many downlink communication subframes percomponent carrier (hereinafter, described as “DL (DownLink) subframes,”“D” or “S” shown in FIG. 3) of results of error detection need to beindicated to the base station using one uplink communication subframe(hereinafter, described as “UL (UpLink) subframe,” “U” shown in FIG. 3).For example, in Config 2 shown in FIG. 3, since results of errordetection of four DL subframes are indicated to the base station usingone UL subframe, M=4.

(1) M=1

(2) M=2

(3) M=3

(4) M=4

That is, FIG. 6A illustrates a method of mapping a pattern for resultsof error detection when (a) to (c) above are combined with (1) to (4)above. The value of M varies depending on UL-DL configuration (Config 0to 6) and subframe number (SF #0 to SF #9) in one frame as shown in FIG.3. Furthermore, in Config 5 shown in FIG. 3, M=9 in subframe (SF) #2.However, in this case, in the LTE-A TDD system, the terminal does notapply channel selection and indicates the results of error detectionusing, for example, a DFT-S-OFDM format. For this reason, in FIG. 6A,Config 5 (M=9) is not included in the combination.

In the case of (1), the number of error detection result patterns is2²×1=4 patterns, 2³×1=8 patterns and 2⁴×1=16 patterns in order of (a),(b) and (c). In the case of (2), the number of error detection resultpatterns is 2²×2=8 patterns, 2³×2=16 patterns, 2⁴×2=32 patterns in orderof (a), (b) and (c). The same applies to (3) and (4).

Here, it is assumed that the phase difference between phase points to bemapped in one PUCCH resource is 90 degrees at minimum (that is, a casewhere a maximum of 4 patterns per PUCCH resource are mapped). In thiscase, the number of PUCCH resources necessary to map all error detectionresult patterns is 2⁴×4÷4=16 in (4) and (c) when the number of errordetection result patterns is a maximum (2⁴×4=64 patterns), which is notrealistic. Thus, the TDD system intentionally reduces the amount ofinformation on the results of error detection by bundling the results oferror detection in a spatial region or further in a time domain ifnecessary. In this way, the TDD system limits the number of PUCCHresources necessary to indicate the error detection result patterns.

In the LTE-A TDD system, in the case of (1), the terminal maps 4patterns, 8 patterns and 16 patterns of results of error detection inorder of (a), (b) and (c) to 2, 3 and 4 PUCCH resources respectivelywithout bundling the results of error detection (Step3 in FIG. 6A). Thatis, the terminal indicates an error detection result using 1 bit percomponent carrier in which a transmission mode (non-MIMO) supportingonly one-CW transmission in downlink and indicates error detectionresults using 2 bits per component carrier in which a transmission mode(MIMO) supporting up to two-CW transmissions in downlink.

In the LTE-A TDD system, in the cases of (2) and (a), the terminal mapseight patterns of results of error detection to four PUCCH resourceswithout bundling the results of error detection (Step3 in FIG. 6A). Inthat case, the terminal indicates error detection results using 2 bitsper downlink component carrier.

In the LTE-A TDD system, in the cases of (2) and (b) (the same appliesto (2) and (c)), the terminal bundles the results of error detection ofcomponent carriers in which a transmission mode supporting up to two-CWtransmission in downlink is set in a spatial region (spatial bundling)(Step 1 in FIG. 6A). In the spatial bundling, when the result of errordetection corresponding to at least one CW of two CWs of the results oferror detection is NACK, the terminal determines the results of errordetection after the spatial bundling to be NACK. That is, in spatialbundling, logical AND of the results of error detection of two CWs istaken. The terminal then maps error detection result patterns afterspatial bundling (8 patterns in the cases of (2) and (b), 16 patterns inthe cases of (2) and (c)) to four PUCCH resources (Step3 in FIG. 6A). Inthat case, the terminal indicates error detection results using 2 bitsper downlink component carrier.

In the LTE-A TDD system, in the cases of (3) or (4), and (a), (b) or(c), the terminal performs bundling in the time domain (time-domainbundling) after the spatial bundling (Step1 in FIG. 6A) (Step2 in FIG.6A). The terminal then maps the error detection result patterns afterthe time-domain bundling to four PUCCH resources (Step3 in FIG. 6A). Inthat case, the terminal indicates results of error detection using 2bits per downlink component carrier.

Next, an example of more specific mapping methods will be described withreference to FIG. 6B. FIG. 6B shows an example of a case where thenumber of downlink component carriers is 2 (one PCell, one SCell) and acase where “(c) a transmission mode in which each component carriersupports up to two-CW downlink transmission” is set and a case with “(4)M=4.”

In FIG. 6B, the results of error detection of a PCell are (ACK (A),ACK), (ACK, ACK), (NACK (N), NACK) and (ACK, ACK) in order of (CW0, CW1)in four DL subframes (SF1 to 4). In the PCell shown in FIG. 6B, M=4, andtherefore the terminal spatially bundles these subframes in Step 1 inFIG. 6A (portions enclosed by a solid line in FIG. 6B). As a result ofthe spatial bundling, ACK, ACK, NACK and ACK are obtained in that orderin four DL subframes of the PCell shown in FIG. 6B. Furthermore, inStep2 in FIG. 6A, the terminal applies time-domain bundling to the 4-biterror detection result pattern (ACK, ACK, NACK, ACK) after spatialbundling obtained in Step 1 (portions enclosed by broken line in FIG.6B). In this way, a 2-bit error detection result of (NACK, ACK) isobtained in the PCell shown in FIG. 6B.

The terminal likewise applies spatial bundling and time-domain bundlingalso for the SCell shown in FIG. 6B and thereby obtains a 2-bit errordetection result (NACK, NACK).

The terminal then combines the error detection result patterns using 2bits each after time-domain bundling of the PCell and SCell in Step3 inFIG. 6A in order of the PCell, SCell to bundle them into a 4-bit errordetection result pattern (NACK, ACK, NACK, NACK). The terminaldetermines a PUCCH resource (in this case, h1) and a phase point (inthis case, -j) using the mapping table shown in Step3 in FIG. 6A fromthis 4-bit error detection result pattern.

The LTE system and LTE-A system support HARQ (Hybrid Automatic RepeatreQuest) (hereinafter, referred to as “DL HARQ”) of downlink data. In DLHARQ, the LTE terminal and LTE-A terminal store an LLR (Log LikelihoodRatio) (or may also be called “soft bit”) for downlink data in which anerror is detected in a soft buffer. The LLR stored in the soft buffer iscombined with an LLR corresponding to downlink data to be retransmitted(retransmission data). The soft buffer (buffer capacity: N_(soft)) asshown in FIG. 7A and following equation 1 is divided into equal portionsbased on the number of downlink component carriers (KO supported by aterminal, the number of multiplexed layers (K_(MIMO)) supported by theterminal, and the maximum number of DL HARQ processes (M_(DL) _(_)_(HARQ)) defined in a UL-DL configuration set in the terminal, and an IR(Incremental Redundancy) buffer size (N_(IR)) per transport block (orTB) is calculated. The maximum number of DL HARQ processes representsthe number of retransmission processes (the number of DL HARQ processes)set based on a maximum value of retransmission interval (may also becalled “RTT (Round Trip Time)”) after transmission of downlink data inDL HARQ in each UL-DL configuration (Config #0 to #6) untilretransmission of the downlink data (see FIG. 7B).

[1] $\begin{matrix}{N_{IR} = \left\lfloor \frac{N_{soft}}{K_{C} \cdot K_{MIMO} \cdot {\min \left( {M_{{DL}_{—}{HARQ}},M_{limit}} \right)}} \right\rfloor} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

The terminal stores the LLR corresponding to the downlink data in whichan error has been detected in an IR buffer corresponding to each DL HARQprocess within a range of IR buffer size per TB calculated according toequation 1. Here, M_(limit) shown in equation 1 is an allowable value ofthe number of DL HARQ processes stored in the soft buffer and the valueof M_(limit) is, for example, 8. To reduce the total capacity of thesoft buffer (soft buffer capacity), the IR buffer per TB cannot alwaysstore all systematic bits (LLR) per TB and all parity bits (LLR).Therefore, increasing the IR buffer size per TB as much as possiblewithin the soft buffer capacity leads to an increase in the total amountof LLR that can be stored in the IR buffer and consequently leads to animprovement of HARQ retransmission performance.

As described above, the LTE-A terminal is designed on the assumptionthat the same UL-DL configuration is set among a plurality of componentcarriers. This is because conventionally, carrier aggregation (so-calledintra-band carrier aggregation) among a plurality of component carriers(e.g., certain component carrier having a 20 MHz bandwidth and anothercomponent carrier having a 20 MHz bandwidth within a 2 GHz band) in onefrequency band (e.g., 2 GHz band) is assumed. That is, when uplinkcommunication and downlink communication are simultaneously performedbetween different component carriers within the same frequency band, aterminal in downlink communication receives large interference from aterminal carrying out uplink communication.

On the other hand, in carrier aggregation (so-called inter-band carrieraggregation) between component carriers (e.g., component carrier havinga 20 MHz bandwidth in a 2 GHz band and component carrier having a 20 MHzbandwidth in an 800 MHz band) of a plurality of frequency bands (e.g., 2GHz band and 800 MHz band), there is a large frequency interval betweenboth component carriers.

Thus, a terminal in downlink communication using a component carrier ina certain frequency band (e.g., component carrier having a 20 MHzbandwidth in a 2 GHz band) receives smaller interference from a terminalin uplink communication using another frequency band (e.g., componentcarrier having a 20 MHz bandwidth in an 800 MHz band).

Incidentally, studies are being carried out, for a case where acommunication carrier providing an LTE-A TDD system newly assigns afrequency band to an LTE-A service, on a possibility of varying a UL-DLconfiguration of the newly assigned frequency band from a UL-DLconfiguration of an existing frequency band depending on a service towhich the communication carrier attaches greater importance. To be morespecific, a communication carrier that attaches greater importance todownlink communication throughput uses a UL-DL configuration having agreater ratio of DL subframes to UL subframes in a new frequency band(e.g., Config 3, 4 or 5 or the like in FIG. 3). This allows a moreflexible system to be constructed.

To realize a low PAPR (Peak to Average Power Ratio) during carrieraggregation in LTE-A, studies are being carried out on a possibility ofa terminal transmitting a response signal (HARQ-ACK) which is an errordetection result corresponding to each piece of downlink data of eachcomponent carrier (PCell and SCell) always using a single componentcarrier (e.g., PCell) only.

However, when different UL-DL configurations are set between componentcarriers, there are timings at which subframes of PCell become DLsubframes and subframes of SCell become UL subframes. At such timings,the terminal cannot transmit any response signal in response to downlinkdata of SCell using PUCCH of PCell. Thus, in LTE-A, studies are beingcarried out on a possibility of using PDSCH-PUCCH timing defined inanother UL-DL configuration (reference UL-DL configuration) instead oftransmission/reception timing (PDSCH-PUCCH timing) between PDSCH(downlink data reception) and PUCCH (response signal transmission)defined in the UL-DL configuration set in SCell.

As shown in FIG. 8, there are inclusion relations regarding DL subframesbetween the UL-DL configurations shown in FIG. 3. A relation betweenConfig #0 and Config #1 will be described as an example first. In FIG.3, DL subframes (including special subframes) included in one frame areSF #0, #1, #5 and #6 in Config #0 and SF #0, #1, #4, #5, #6 and #9 inConfig #1. That is, a set of DL subframes included in one frame ofConfig #1 includes a set of DL subframes included in one frame of Config#0. That is, the set of DL subframes of Config #1 can be said to be asuperset of DL subframes of Config #0. Alternatively, the set of DLsubframes of Config #0 can also be said to be a subset of DL subframesof Config #1. In the following description, in Config #1, for example,in such a combination of UL-DL configurations in which DL subframes areset at least at the same timings as those of DL subframes of Config #0,Config #1 may be expressed as “DL heavier” than Config #0. Furthermore,the set of UL subframes of Config #0 may also be said to include the setof UL subframes of Config #1 (superset of UL subframes) (not shown).Therefore, in the following description, for example, in such acombination of UL-DL configurations in which UL subframes are set at thesame timings as those of UL subframes of Config #1 at least, Config #0may also be expressed as “UL heavier” than Config #1.

Next, a relationship between Config #1 and Config #3 will be described.In FIG. 3, DL subframes (including special subframes) included in oneframe are SF #0, #1 and #5 to #9 in Config #3. That is, there ismutually no inclusion relation between sets of DL subframes of Config #1and Config #3. That is, the set of DL subframes of Config #1 can be saidto be neither superset nor subset of DL subframes of Config #3. In thefollowing description, in a combination of UL-DL configurations in whichDL subframes and UL subframes set at different timings are set in Config#1 and Config #3 at least, Config #1 may be expressed as neither “DLheavy nor UL heavy” with respect to Config #3. Inclusion relationsregarding DL subframes similar to those described above also existbetween other UL-DL configurations (see FIG. 8).

FIGS. 9A and 9B illustrate an example of PDSCH-PUCCH timings when a setof DL subframes of PCell included in one frame includes a set of DLsubframes of SCell (that is, when the set of DL subframe of PCell is asuperset of DL subframes of SCell or a UL-DL configuration of PCell isDL heavier than a UL-DL configuration of SCell). In FIG. 9A and FIG. 9B,Config #1 is set in PCell and Config #0 is set in SCell.

Hereinafter, a case where the UL-DL configuration of PCell is DL heavierthan the UL-DL configuration of SCell may be expressed as “PCell is DLheavy.”

FIG. 9A illustrates a case where SCell references PDSCH-PUCCH timingdefined in Config #0 set in SCell. In this case, in Config #0 set inSCell, despite the UL subframe in which PUCCH (response signal)corresponding to PDSCH (downlink data) is transmitted, there are timingsat which subframes become DL subframes in Config #1 set in PCell(subframes #4 and #9 in FIG. 9A). PUCCH transmission in PCellcorresponding to PDSCH of SCell cannot be performed at this timing.Therefore, it is not possible to use any DL subframe of SCell (subframes#0 and #5 in FIG. 9A) corresponding to this timing to indicate PDSCH.

On the other hand, FIG. 9B illustrates a case where SCell referencesPDSCH-PUCCH timing defined in Config #1 set in PCell. In this case,subframes of PCell never become DL subframes at timings at which PUCCH(response signal) corresponding to PDSCH (downlink data) of SCell istransmitted. Therefore, PUCCH transmission in PCell corresponding toPDSCH in SCell can always be performed. Therefore, all DL subframes inSCell can be used to indicate PDSCH. Thus, in FIG. 9B, since there is notiming at which PUCCH transmission in PCell corresponding to PDSCH ofSCell cannot be performed in PCell, all DL subframes in SCell can beused.

Next, FIGS. 10A and 10B each illustrate an example of PDSCH-PUCCH timingin a case where a set of DL subframes of PCell included in one frameincludes no set of DL subframes of SCell and is not included in the setof DL subframes of SCell (that is, when the set of DL subframes of PCellis neither superset nor subset of DL subframes of SCell or PCell isneither DL heavy nor UL heavy). In FIG. 10A and FIG. 10B, Config #1 isset in PCell and Config #3 is set in SCell.

FIG. 10A illustrates a case where SCell references PDSCH-PUCCH timingsdefined in Config #1 set in PCell. In this case, as in the case of FIG.9B, subframes of PCell never become DL subframes at timings at whichPUCCH corresponding to PDSCH of SCell is transmitted. Thus, in FIG. 10A,there is no DL subframe of SCell that can no longer be used due toinability for PCell to transmit PUCCH corresponding to PDSCH of SCell.However, there are cases where DL subframes of SCell cannot be usedbecause PDSCH-PUCCH timings are not defined in Config #1 set in PCell.For example, while subframes #7 and #8 shown in FIG. 10A are DLsubframes in SCell, they are UL subframes in PCell. Thus, PDSCH-PUCCHtimings at which subframes #7 and 8 become DL subframes are notoriginally defined in Config #1 set in PCell. For this reason, DLsubframes of SCell cannot be used to indicate PDSCH in subframes #7 and8.

In contrast, FIG. 10B illustrates a case where SCell referencesPDSCH-PUCCH timings defined in a UL-DL configuration (Config #4) havinga maximum number of DL subframes among UL-DL configurations which aresupersets of DL subframes of both Config #1 set in PCell and Config #3set in SCell.

There are three combinations of UL-DL configurations in which twocomponent carriers are neither DL heavy nor UL heavy: Config #1 andConfig #3, Config #2 and Config #3, and Config #2 and Config #4 (seeFIG. 8). At this time, when one component carrier is Config #1 and theother component carrier is Config #3 (see FIG. 10B), a UL-DLconfiguration referenced by SCell is assumed to be Config #4.Furthermore, when one component carrier is Config #2 and the othercomponent carrier is Config #3, a UL-DL configuration referenced bySCell is assumed to be Config #5. On the other hand, when one componentcarrier is Config #2 and the other component carrier is Config #4, aUL-DL configuration referenced by SCell is assumed to be Config #5.

By so doing, there is no timing in PCell at which PUCCH corresponding toPDSCH of SCell cannot be transmitted. Furthermore, there will be no casewhere DL subframes of SCell cannot be used due to inability for PCell todefine the PDSCH-PUCCH timings described above. For this reason, SCellcan use all DL subframes.

FIG. 11 illustrates an example of PDSCH-PUCCH timings when a set of DLsubframes of PCell included in one frame is included in a set of DLsubframes of SCell (that is, when a set of DL subframes of PCell is asubset of DL subframes of SCell or when PCell is UL heavy). In thiscase, SCell references PDSCH-PUCCH timings defined in Config #1 set inSCell, and can thereby use all DL subframes of SCell.

In the LTE-A system, studies are being carried out on a possibility ofchanging UL-DL configurations (hereinafter may be referred to as “TDDeIMTA (enhancement for DL-UL Interference Management and TrafficAdaptation).” Examples of objects of TDD eIMTA include provision of aservice that meets the needs of users by a flexible change of a UL/DLratio, a reduction of power consumption in a base station by increasinga UL ratio in a time zone with a low traffic load or the like. As amethod of changing a UL-DL configuration, studies are being carried outon (1) a method by indicating an SI (System Information) signaling base,(2) a method by indicating an RRC (higher layer) signaling base and (3)a method by indicating an L1 (Physical Layer) signaling base.

Method (1) corresponds to a change of a UL-DL configuration with thelowest frequency. Method (1) is suitable for cases where an objective isto reduce power consumption in a base station by increasing a UL ratio,for example, in a time zone with a low traffic load (e.g., midnight orearly morning). Method (3) corresponds to a change of a UL-DLconfiguration with the highest frequency. A small cell such as a picocell has fewer terminals to be connected than a large cell such as amacro cell. In a pico cell, UL/DL traffic of the entire pico cell isdetermined depending on the amount of UL/DL traffic in a small number ofterminals connected to the pico cell. For this reason, a violent timefluctuation in UL/DL traffic occurs in the pico cell. Therefore, method(3) is suitable for a case where a UL-DL configuration is changed inaccordance with a time fluctuation in UL/DL traffic in a small cell likea pico cell. Method (2) may be positioned between method (1) and method(3) and is suitable for a case where a UL-DL configuration is changedwith a medium degree of frequency.

CITATION LIST Non-Patent Literature

NPL 1

3GPP TS 36.211 V10.1.0, “Physical Channels and Modulation (Release 10),”March 2011

NPL 2

3GPP TS 36.212 V10.1.0, “Multiplexing and channel coding (Release 10),”March 2011

NPL 3

3GPP TS 36.213 V10.1.0, “Physical layer procedures (Release 10),” March2011

NPL 4

Seigo Nakao, Tomofumi Takata, Daichi Imamura, and Katsuhiko Hiramatsu,“Performance enhancement of E-UTRA uplink control channel in fast fadingenvironments,” Proceeding of IEEE VTC 2009 spring, April. 2009

NPL 5

Ericsson and ST-Ericsson, “A/N transmission in the uplink for carrieraggregation,” R1-100909, 3GPP TSG-RAN WG1 #60, February 2010

NPL 6

ZTE, 3GPP RANI meeting #57, R1-091702, “Uplink Control Channel Designfor LTE-Advanced,” May 2009

NPL 7

Panasonic, 3GPP RANI meeting #57, R1-091744, “UL ACK/NACK transmissionon PUCCH for Carrier aggregation,” May 2009

BRIEF SUMMARY Technical Problem

As described above, DL HARQ regarding downlink data needs to besupported even when a UL-DL configuration varies among a plurality ofcomponent carriers. As an example, FIG. 12A shows a DL HARQ process whena base station assigns downlink data to a terminal so that the maximumnumber of DL HARQ processes is taken. FIG. 12A illustrates a case wherePCell is DL heavy as shown in FIG. 9B and a case where SCell referencesPDSCH-PUCCH timings defined in a UL-DL configuration set in PCell.Furthermore, for a comparison with FIG. 12A, FIG. 13A shows an exampleof DL HARQ processes in a case where a base station assigns downlinkdata to a terminal so as to take the maximum number of DL HARQ processesin a component carrier (cell) in which Config #0 is set when carrieraggregation is not set (non-CA period).

Note that encircled numbers in FIG. 12A and FIG. 13A show DL HARQprocess numbers. On the other hand, solid line arrows show PDSCH-PUCCHtimings. Broken line arrows show timings between reception of PUCCH(response signal) at a base station and retransmission of PDSCH(downlink data) for the PUCCH (hereinafter, may also be referred to as“PUCCH-PDSCH timing”). Note that PDSCH-PUCCH timing and PUCCH-PDSCHtiming may be expressed as DL HARQ timing. For example, a time intervalrequired from PUCCH reception to PDSCH retransmission is 4 ms (4subframes) or more. Furthermore, the time required from PDSCHtransmission to PDSCH retransmission is expressed as PDSCH RTT (roundtrip time).

Both SCell in which Config #0 is set in FIG. 12A and a component carrierin which Config #0 is set in FIG. 13A have four DL subframes (includingspecial subframes) per frame. However, PDSCH RTT in FIG. 12A isdifferent from that in FIG. 13A. To be more specific, PDSCH RTT is 10 msfor all DL HARQ processes in FIG. 13A. In contrast, PDSCH RTT of each DLHARQ process is 11 ms or 14 ms in FIG. 12A. For this reason, in FIG.13A, since PDSCH RTT is 10 ms for four DL subframes per frame (10 ms), amaximum of four DL HARQ processes are sufficient. This corresponds tothe fact in FIG. 7B that the maximum number of DL HARQ processes inConfig #0 is four. On the other hand, since PDSCH RTT in FIG. 12A isgreater than 10 ms, more than four DL HARQ processes are necessary. Tobe more specific, in the case of FIG. 12A, a maximum of five DL HARQprocesses are necessary.

The reason that more DL HARQ processes are necessary is that SCellreferences PDSCH-PUCCH timings defined in a UL-DL configuration which isDL heavier than a UL-DL configuration set in SCell itself. In otherwords, this is because SCell references PDSCH-PUCCH timings defined inthe UL-DL configuration which has fewer UL subframes and fewer chancesof PUCCH transmission than the UL-DL configuration set in SCell.

As shown in FIG. 7A and FIG. 7B, a DL HARQ soft buffer is divided basedon the maximum number of DL HARQ processes (M_(DL) _(_) _(HARQ)) definedin the UL-DL configuration set in the terminal (see equation 1). Forexample, FIG. 13B illustrates the SCell soft buffer in FIG. 13A. Asshown in FIG. 13B, when the UL-DL configuration set in SCell is Config#0 and the maximum number of DL HARQ processes of SCell is four, theSCell soft buffer is divided into four.

On the other hand, FIG. 12B illustrates the SCell soft buffer in FIG.12A. As shown in FIG. 12B, since the UL-DL configuration set in SCell isConfig #0, the SCell soft buffer is divided into four as in the case ofFIG. 13B. However, as shown in FIG. 12A, when SCell referencesPDSCH-PUCCH timings defined in a UL-DL configuration which is DL heavierthan the UL-DL configuration set in SCell, the maximum number of DL HARQprocesses in SCell is greater than the value shown in FIG. 7B (valueduring a non-CA period). To be more specific, when PDSCH-PUCCH timingreferenced by SCell is timing of Config #1, the maximum number of DLHARQ processes actually required in SCell is five. For this reason, asshown in FIG. 12B, the terminal cannot allocate any IR buffer to some DLHARQ processes (DL HARQ process number 5 in FIG. 13B). Thus, it is notpossible to obtain any coding gain by HARQ retransmission for the DLHARQ processes to which no IR buffer is allocated.

As described above, it is when SCell references PDSCH-PUCCH timingsdefined in a UL-DL configuration which is DL heavier than the UL-DLconfiguration set in SCell that the maximum number of DL HARQ processeswhich is actually required in SCell becomes greater than the maximumnumber of DL HARQ processes defined in the UL-DL configuration set inSCell. Therefore, not only when PCell is DL heavy but also when PCell isneither DL heavy nor UL heavy (FIG. 10B), the maximum number of DL HARQprocesses which is actually required in SCell becomes greater than themaximum number of DL HARQ processes defined in the UL-DL configurationset in SCell. Thus, problems similar to those described above exist alsowhen PCell is neither DL heavy nor UL heavy.

As described above, when SCell references PDSCH-PUCCH timings defined ina UL-DL configuration which is DL heavier than the UL-DL configurationset in SCell, there is a case where the IR buffer is not allocated tosome DL HARQ processes and it is not possible to obtain any coding gainthrough HARQ retransmission.

An object of the present invention is to provide a terminal apparatusand a buffer dividing method capable of obtaining a coding gain by HARQfor all DL HARQ processes even when a UL-DL configuration differs amonga plurality of component carriers.

Solution to Problem

A terminal apparatus according to an aspect of the present invention isan apparatus which communicates with a base station apparatus using aplurality of component carriers and for which a configuration pattern ofsubframes included in one frame is set for each of the plurality ofcomponent carriers, the configuration pattern including a downlinkcommunication subframe used for downlink communication and an uplinkcommunication subframe used for uplink communication, the terminalapparatus including: a decoding section that stores, in a retransmissionbuffer, downlink data transmitted in each of the plurality of componentcarriers and decodes the downlink data; a generating section thatgenerates a response signal using a result of error detection of thedownlink data; and a transmitting section that transmits, using a firstcomponent carrier of the plurality of component carriers, a responsesignal for first downlink data received using the first componentcarrier and a response signal for second downlink data received using asecond component carrier of the plurality of component carriers, inwhich: the buffer includes a first buffer that stores the first downlinkdata and a second buffer that stores the second downlink data; and thesecond buffer is divided into regions respectively corresponding toretransmission processes based on a specific value determined by acombination of a first configuration pattern that is set in the firstcomponent carrier and a second configuration pattern that is set in thesecond component carrier.

A buffer dividing method according to an aspect of the present inventionis a method for a terminal apparatus which communicates with a basestation apparatus, using a plurality of component carriers and in whicha configuration pattern of subframes included in one frame is set foreach of the plurality of component carriers, the configuration patternincluding a downlink communication subframe used for downlinkcommunication and an uplink communication subframe used for uplinkcommunication, the method including: storing, in a retransmissionbuffer, downlink data transmitted in each of the plurality of componentcarriers; decoding the downlink data; generating a response signal usinga result of error detection of the downlink data; and transmitting,using a first component carrier of the plurality of component carriers,a response signal for first downlink data received in the firstcomponent carrier and a response signal for second downlink datareceived in a second component carrier of the plurality of componentcarriers, in which: the buffer includes a first buffer that stores thefirst downlink data and a second buffer that stores the second downlinkdata; and the second buffer is divided into regions respectivelycorresponding to retransmission processes based on a specific valuedetermined by a combination of a first configuration pattern that is setin the first component carrier and a second configuration pattern thatis set in the second component carrier.

Advantageous Effects of Invention

According to the present invention, it is possible to obtain a codinggain by HARQ for all DL HARQ processes even when a UL-DL configurationdiffers among a plurality of component carriers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating a method of spreading response signalsand reference signals;

FIG. 2 is a diagram illustrating an operation related to a case whereTDM is applied to response signals and uplink data on PUSCH resources;

FIG. 3 is a diagram provided for describing a UL-DL configuration inTDD;

FIGS. 4A and 4B are diagrams provided for describing asymmetric carrieraggregation and a control sequence applied to individual terminals;

FIG. 5 is a diagram provided for describing channel selection;

FIGS. 6A and 6B are diagrams provided for describing a bundling methodand a mapping method in TDD;

FIGS. 7A and 7B are diagrams provided for describing division of a softbuffer and determination of the maximum number of DL HARQ processes;

FIG. 8 is a diagram provided for describing inclusion relations of DLsubframes among UL-DL configurations;

FIGS. 9A and 9B are diagrams provided for describing SCell referencetimings when PCell is DL heavy;

FIGS. 10A and 10B are diagrams provided for describing SCell referencetimings when PCell is neither DL heavy nor UL heavy;

FIG. 11 is a diagram provided for describing SCell reference timingswhen PCell is UL heavy;

FIGS. 12A and 12B are diagrams provided for describing a problem whenPCell is DL heavy;

FIGS. 13A and 13B are diagrams provided for describing a problem when

PCell is DL heavy;

FIG. 14 is a block diagram illustrating a main configuration of aterminal according to Embodiment 1 of the present invention;

FIG. 15 is a block diagram illustrating a configuration of a basestation according to Embodiment 1 of the present invention;

FIG. 16 is a block diagram illustrating a configuration of a terminalaccording to Embodiment 1 of the present invention;

FIGS. 17A to 17C are diagrams provided for describing a setting range ofthe maximum number of DL HARQ processes referenced by SCell according toEmbodiment 1 of the present invention;

FIG. 18 is a diagram illustrating PDSCH RTT corresponding to a UL-DLconfiguration according to Embodiment 1 of the present invention;

FIGS. 19A and 19B are diagrams illustrating the maximum number of DLHARQ processes referenced by SCell according to Embodiment 1 of thepresent invention;

FIG. 20 is a diagram provided for describing a soft buffer dividingmethod according to Embodiment 1 of the present invention;

FIG. 21 is a diagram illustrating results of comparison in minimumvalues between the maximum number of DL HARQ processes referenced bySCell and a constraint value of the maximum number of DL HARQ processesaccording to Embodiment 1 of the present invention;

FIGS. 22A and 22B are diagrams provided for describing a method ofsimply determining the maximum number of DL HARQ processes referenced bySCell according to Embodiment 2 of the present invention;

FIGS. 23A and 23B are diagrams provided for describing timingsreferenced by SCell when cross-carrier scheduling is set;

FIG. 24 is a diagram provided for describing a problem whencross-carrier scheduling is set;

FIG. 25 is a diagram illustrating the maximum number of DL HARQprocesses referenced by SCell when cross-carrier scheduling is setaccording to Embodiment 3 of the present invention;

FIG. 26 is a diagram provided for describing a problem when TDD eIMTA isset; and

FIGS. 27A and 27B are diagrams provided for describing a method ofdetermining the maximum number of DL HARQ processes referenced by SCellwhen TDD eIMTA is set according to Embodiment 4 of the presentinvention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. Throughout theembodiments, the same elements are assigned the same reference numeralsand any duplicate description of the elements is omitted.

Embodiment 1

FIG. 14 is a main configuration diagram of terminal 200 according to thepresent embodiment. Terminal 200 communicates with base station 100using a plurality of component carriers. Furthermore, as a configurationpattern of subframes included in one frame, the configuration patternincluding downlink communication subframes (DL subframes) used fordownlink communication and uplink communication subframes (UL subframes)used for uplink communication (UL-DL Configuration) is set in eachcomponent carrier set for terminal 200. In terminal 200, decodingsection 210 stores downlink data respectively transmitted in a pluralityof component carriers in a retransmission buffer (soft buffer) anddecodes the downlink data, response signal generating section 212generates a response signal using results of error detection of thedownlink data, radio transmitting section 222 transmits a responsesignal corresponding to first downlink data received in a firstcomponent carrier (PCell) of the plurality of component carriers and aresponse signal corresponding to second downlink data received in asecond component carrier (PCell) using the first component carrier.Here, the above-described soft buffer includes a first buffer (PCellsoft buffer) that stores first downlink data and a second buffer (SCellsoft buffer) that stores second downlink data, and the second buffer isdivided into regions respectively corresponding to retransmissionprocesses (IR buffers) based on a specific value (maximum UL-DLconfiguration to be referenced) determined by a combination of a firstconfiguration pattern set in the first component carrier and a secondconfiguration pattern set in the second component carrier.

(Configuration of Base Station)

FIG. 15 is a configuration diagram of base station 100 according toEmbodiment 1 of the present invention. In FIG. 15, base station 100includes control section 101, control information generating section102, coding section 103, modulation section 104, coding section 105,data transmission controlling section 106, modulation section 107,mapping section 108, inverse fast Fourier transform (IFFT) section 109,CP adding section 110, radio transmitting section 111, radio receivingsection 112, CP removing section 113, PUCCH extracting section 114,despreading section 115, sequence controlling section 116, correlationprocessing section 117, A/N determining section 118, bundled A/Ndespreading section 119, inverse discrete Fourier transform (IDFT)section 120, bundled A/N determining section 121 and retransmissioncontrol signal generating section 122.

Control section 101 assigns a downlink resource for transmitting controlinformation (i.e., downlink control information assignment resource) anda downlink resource for transmitting downlink data (i.e., downlink dataassignment resource) for a resource assignment target terminal(hereinafter, referred to as “destination terminal” or simply“terminal”) 200. This resource assignment is performed in a downlinkcomponent carrier included in a component carrier group configured forresource assignment target terminal 200. In addition, the downlinkcontrol information assignment resource is selected from among theresources corresponding to downlink control channel (i.e., PDCCH) ineach downlink component carrier. Moreover, the downlink data assignmentresource is selected from among the resources corresponding to downlinkdata channel (i.e., PDSCH) in each downlink component carrier. Inaddition, when there are a plurality of resource assignment targetterminals 200, control section 101 assigns different resources toresource assignment target terminals 200, respectively.

The downlink control information assignment resources are equivalent toL1/L2 CCH described above. To put it more specifically, the downlinkcontrol information assignment resources are each formed of one or aplurality of CCEs.

Control section 101 determines the coding rate used for transmittingcontrol information to resource assignment target terminal 200. The datasize of the control information varies depending on the coding rate.Thus, control section 101 assigns a downlink control informationassignment resource having the number of CCEs that allows the controlinformation having this data size to be mapped to the resource.

Control section 101 outputs information on the downlink data assignmentresource to control information generating section 102. Moreover,control section 101 outputs information on the coding rate to codingsection 103. In addition, control section 101 determines and outputs thecoding rate of transmission data (i.e., downlink data) to coding section105. Moreover, control section 101 outputs information on the downlinkdata assignment resource and downlink control information assignmentresource to mapping section 108. However, control section 101 controlsthe assignment in such a way that the downlink data and downlink controlinformation for the downlink data are mapped to the same downlinkcomponent carrier.

Control information generating section 102 generates and outputs controlinformation including the information on the downlink data assignmentresource to coding section 103. This control information is generatedfor each downlink component carrier. In addition, when there are aplurality of resource assignment target terminals 200, the controlinformation includes the terminal ID of each destination terminal 200 inorder to distinguish resource assignment target terminals 200 from oneanother. For example, the control information includes CRC bits maskedby the terminal ID of destination terminal 200. This control informationmay be referred to as “control information carrying downlink assignment”or “downlink control information (DCI).” Control information generatingsection 102 references, for example, the retransmission control signal(not shown) generated by retransmission control signal generatingsection 122 and includes, in the control information, retransmissioninformation indicating whether transmission of downlink data whosetransmission is controlled by data transmission controlling section 106is initial transmission or retransmission.

Coding section 103 encodes the control information using the coding ratereceived from control section 101 and outputs the coded controlinformation to modulation section 104.

Modulation section 104 modulates the coded control information andoutputs the resultant modulation signals to mapping section 108.

Coding section 105 uses the transmission data (i.e., downlink data) foreach destination terminal 200 and the coding rate information fromcontrol section 101 as input and encodes and outputs the transmissiondata to data transmission controlling section 106.

However, when a plurality of downlink component carriers are assigned todestination terminal 200, coding section 105 encodes each piece oftransmission data to be transmitted on a corresponding one of thedownlink component carriers and transmits the coded pieces oftransmission data to data transmission controlling section 106.

Data transmission controlling section 106 outputs the coded transmissiondata to modulation section 107 and also keeps the coded transmissiondata at the initial transmission. In addition, data transmissioncontrolling section 106 keeps the transmission data for one destinationterminal 200 for each downlink component carrier on which thetransmission data is transmitted. Thus, it is possible to perform notonly retransmission control for overall data transmitted to destinationterminal 200, but also retransmission control for data on each downlinkcomponent carrier.

Furthermore, upon reception of a NACK or DTX for downlink datatransmitted on a certain downlink component carrier from retransmissioncontrol signal generating section 122, data transmission controllingsection 106 outputs the data kept in the manner described above andcorresponding to this downlink component carrier to modulation section107. Upon reception of an ACK for the downlink data transmitted on acertain downlink component carrier from retransmission control signalgenerating section 122, data transmission controlling section 106deletes the data kept in the manner described above and corresponding tothis downlink component carrier.

Modulation section 107 modulates the coded transmission data receivedfrom data transmission controlling section 106 and outputs the resultantmodulation signals to mapping section 108.

Mapping section 108 maps the modulation signals of the controlinformation received from modulation section 104 to the resourceindicated by the downlink control information assignment resourcereceived from control section 101 and outputs the resultant modulationsignals to IFFT section 109.

Mapping section 108 maps the modulation signals of the transmission datareceived from modulation section 107 to the resource (i.e., PDSCH (i.e.,downlink data channel)) indicated by the downlink data assignmentresource received from control section 101 (i.e., information includedin the control information) and outputs the resultant modulation signalsto IFFT section 109.

The control information and transmission data mapped to a plurality ofsubcarriers in a plurality of downlink component carriers in mappingsection 108 is transformed into time-domain signals fromfrequency-domain signals in IFFT section 109, and CP adding section 110adds a CP to the time-domain signals to form OFDM signals. The OFDMsignals undergo transmission processing such as digital to analog (D/A)conversion, amplification and up-conversion and/or the like in radiotransmitting section 111 and are transmitted to terminal 200 via anantenna.

Radio receiving section 112 receives, via an antenna, the uplinkresponse signals or reference signals transmitted from terminal 200, andperforms reception processing such as down-conversion, A/D conversionand/or the like on the uplink response signals or reference signals.

CP removing section 113 removes the CP added to the uplink responsesignals or reference signals from the uplink response signals orreference signals that have undergone the reception processing.

PUCCH extracting section 114 extracts, from the PUCCH signals includedin the received signals, the signals in the PUCCH region correspondingto the bundled ACK/NACK resource previously indicated to terminal 200.The bundled ACK/NACK resource herein refers to a resource used fortransmission of the bundled ACK/NACK signals and adopting the DFT-S-OFDMformat structure. To put it more specifically, PUCCH extracting section114 extracts the data part of the PUCCH region corresponding to thebundled ACK/NACK resource (i.e., SC-FDMA symbols on which the bundledACK/NACK resource is assigned) and the reference signal part of thePUCCH region (i.e., SC-FDMA symbols on which the reference signals fordemodulating the bundled ACK/NACK signals are assigned). PUCCHextracting section 114 outputs the extracted data part to bundled A/Ndespreading section 119 and outputs the reference signal part todespreading section 115-1.

In addition, PUCCH extracting section 114 extracts, from the PUCCHsignals included in the received signals, a plurality of PUCCH regionscorresponding to an A/N resource associated with a CCE that has beenoccupied by the PDCCH used for transmission of the downlink assignmentcontrol information (DCI), and corresponding to a plurality of A/Nresources previously indicated to terminal 200. The A/N resource hereinrefers to the resource to be used for transmission of an A/N. To put itmore specifically, PUCCH extracting section 114 extracts the data partof the PUCCH region corresponding to the A/N resource (i.e., SC-FDMAsymbols on which the uplink control signals are assigned) and thereference signal part of the PUCCH region (i.e., SC-FDMA symbols onwhich the reference signals for demodulating the uplink control signalsare assigned). PUCCH extracting section 114 outputs both of theextracted data part and reference signal part to despreading section115-2. In this manner, the response signals are received on the resourceselected from the PUCCH resource associated with the CCE and thespecific PUCCH resource previously indicated to terminal 200.

Sequence controlling section 116 generates a base sequence that may beused for spreading each of the A/N indicated from terminal 200, thereference signals for the A/N, and the reference signals for the bundledACK/NACK signals (i.e., length-12 ZAC sequence). In addition, sequencecontrolling section 116 identifies a correlation window corresponding toa resource on which the reference signals may be assigned (hereinafter,referred to as “reference signal resource”) in PUCCH resources that maybe used by terminal 200. Sequence controlling section 116 outputs theinformation indicating the correlation window corresponding to thereference signal resource on which the reference signals may be assignedin bundled ACK/NACK resources and the base sequence to correlationprocessing section 117-1. Sequence controlling section 116 outputs theinformation indicating the correlation window corresponding to thereference signal resource and the base sequence to correlationprocessing section 117-1. In addition, sequence controlling section 116outputs the information indicating the correlation window correspondingto the A/N resources on which an A/N and the reference signals for theA/N are assigned and the base sequence to correlation processing section117-2.

Despreading section 115-1 and correlation processing section 117-1perform processing on the reference signals extracted from the PUCCHregion corresponding to the bundled ACK/NACK resource.

To put it more specifically, despreading section 115-1 despreads thereference signal part using a Walsh sequence to be used insecondary-spreading for the reference signals of the bundled ACK/NACKresource by terminal 200 and outputs the despread signals to correlationprocessing section 117-1.

Correlation processing section 117-1 uses the information indicating thecorrelation window corresponding to the reference signal resource andthe base sequence and thereby finds a correlation value between thesignals received from despreading section 115-1 and the base sequencethat may be used in primary-spreading in terminal 200. Correlationprocessing section 117-1 outputs the correlation value to bundled A/Ndetermining section 121.

Despreading section 115-2 and correlation processing section 117-2perform processing on the reference signals and A/Ns extracted from theplurality of PUCCH regions corresponding to the plurality of A/Nresources.

To put it more specifically, despreading section 115-2 despreads thedata part and reference signal part using a Walsh sequence and a DFTsequence to be used in secondary-spreading for the data part andreference signal part of each of the A/N resources by terminal 200, andoutputs the despread signals to correlation processing section 117-2.

Correlation processing section 117-2 uses the information indicating thecorrelation window corresponding to each of the A/N resources and thebase sequence and thereby finds a correlation value between the signalsreceived from despreading section 115-2 and a base sequence that may beused in primary-spreading by terminal 200. Correlation processingsection 117-2 outputs each correlation value to A/N determining section118.

A/N determining section 118 determines, on the basis of the plurality ofcorrelation values received from correlation processing section 117-2,which of the A/N resources is used to transmit the signals from terminal200 or none of the A/N resources is used. When determining that thesignals are transmitted using one of the A/N resources from terminal200, A/N determining section 118 performs coherent detection using acomponent corresponding to the reference signals and a componentcorresponding to the A/N and outputs the result of coherent detection toretransmission control signal generating section 122. Meanwhile, whendetermining that terminal 200 uses none of the A/N resources, A/Ndetermining section 118 outputs the determination result indicating thatnone of the A/N resources is used to retransmission control signalgenerating section 122.

Bundled A/N despreading section 119 despreads, using a DFT sequence, thebundled ACK/NACK signals corresponding to the data part of the bundledACK/NACK resource received from PUCCH extracting section 114 and outputsthe despread signals to IDFT section 120.

IDFT section 120 transforms the bundled ACK/NACK signals in thefrequency-domain received from bundled A/N despreading section 119 intotime-domain signals by IDFT processing and outputs the bundled ACK/NACKsignals in the time-domain to bundled A/N determining section 121.

Bundled A/N determining section 121 demodulates the bundled ACK/NACKsignals corresponding to the data part of the bundled ACK/NACK resourcereceived from IDFT section 120, using the reference signal informationon the bundled ACK/NACK signals that is received from correlationprocessing section 117-1. In addition, bundled A/N determination section121 decodes the demodulated bundled ACK/NACK signals and outputs theresult of decoding to retransmission control signal generating section122 as the bundled A/N information. However, when the correlation valuereceived from correlation processing section 117-1 is smaller than athreshold, and bundled A/N determining section 121 thus determines thatterminal 200 does not use any bundled A/N resource to transmit thesignals, bundled A/N determining section 121 outputs the result ofdetermination to retransmission control signal generating section 122.

Retransmission control signal generating section 122 determines whetheror not to retransmit the data transmitted on the downlink componentcarrier (i.e., downlink data) on the basis of the information inputtedfrom bundled A/N determining section 121 and the information inputtedfrom A/N determining section 118 and generates retransmission controlsignals based on the result of determination. To put it morespecifically, when determining that downlink data transmitted on acertain downlink component carrier needs to be retransmitted,retransmission control signal generating section 122 generatesretransmission control signals indicating a retransmission command forthe downlink data and outputs the retransmission control signals to datatransmission controlling section 106. In addition, when determining thatthe downlink data transmitted on a certain downlink component carrierdoes not need to be retransmitted, retransmission control signalgenerating section 122 generates retransmission control signalsindicating not to retransmit the downlink data transmitted on thedownlink component carrier and outputs the retransmission controlsignals to data transmission controlling section 106.

(Configuration of Terminal)

FIG. 16 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1. In FIG. 16, terminal 200 includes radioreceiving section 201, CP removing section 202, fast Fourier transform(FFT) section 203, extraction section 204, demodulation section 205,decoding section 206, determination section 207, control section 208,demodulation section 209, decoding section 210, CRC section 211,response signal generating section 212, coding and modulation section213, primary-spreading sections 214-1 and 214-2, secondary-spreadingsections 215-1 and 215-2, DFT section 216, spreading section 217, IFFTsections 218-1, 218-2 and 218-3, CP adding sections 219-1, 219-2 and219-3, time-multiplexing section 220, selection section 221 and radiotransmitting section 222.

Radio receiving section 201 receives, via an antenna, OFDM signalstransmitted from base station 100 and performs reception processing suchas down-conversion, A/D conversion and/or the like on the received OFDMsignals. It should be noted that, the received OFDM signals includePDSCH signals assigned to a resource in a PDSCH (i.e., downlink data),or PDCCH signals assigned to a resource in a PDCCH.

CP removing section 202 removes a CP that has been added to the OFDMsignals from the OFDM signals that have undergone the receptionprocessing.

FFT section 203 transforms the received OFDM signals intofrequency-domain signals by FFT processing and outputs the resultantreceived signals to extraction section 204.

Extraction section 204 extracts, from the received signals to bereceived from FFT section 203, downlink control channel signals (i.e.,PDCCH signals) in accordance with coding rate information to bereceived. To put it more specifically, the number of CCEs forming adownlink control information assignment resource varies depending on thecoding rate. Thus, extraction section 204 uses the number of CCEs thatcorresponds to the coding rate as units of extraction processing, andextracts downlink control channel signals. In addition, the downlinkcontrol channel signals are extracted for each downlink componentcarrier. The extracted downlink control channel signals are outputted todemodulation section 205.

Extraction section 204 extracts downlink data (i.e., downlink datachannel signals (i.e., PDSCH signals)) from the received signals on thebasis of information on the downlink data assignment resource intendedfor terminal 200 to be received from determination section 207 to bedescribed, hereinafter, and outputs the downlink data to demodulationsection 209. As described above, extraction section 204 receives thedownlink assignment control information (i.e., DCI) mapped to the PDCCHand receives the downlink data on the PDSCH.

Demodulation section 205 demodulates the downlink control channelsignals received from extraction section 204 and outputs the obtainedresult of demodulation to decoding section 206.

Decoding section 206 decodes the result of demodulation received fromdemodulation section 205 in accordance with the received coding rateinformation and outputs the obtained result of decoding to determinationsection 207.

Determination section 207 performs blind-determination (i.e.,monitoring) to find out whether or not the control information includedin the result of decoding received from decoding section 206 is thecontrol information intended for terminal 200. This determination ismade in units of decoding results corresponding to the units ofextraction processing. For example, determination section 207 demasksthe CRC bits by the terminal ID of terminal 200 and determines that thecontrol information resulted in CRC=OK (no error) as the controlinformation intended for terminal 200.

Determination section 207 outputs information on the downlink dataassignment resource intended for terminal 200, which is included in thecontrol information intended for terminal 200, to extraction section204.

Furthermore, determination section 207 outputs retransmissioninformation included in the control information intended for terminal200 indicating whether transmission of downlink data to terminal 200 isinitial transmission or retransmission to decoding section 210.

In addition, when detecting the control information (i.e., downlinkassignment control information) intended for terminal 200, determinationsection 207 informs control section 208 that ACK/NACK signals will begenerated (or are present). Moreover, when detecting the controlinformation intended for terminal 200 from PDCCH signals, determinationsection 207 outputs information on a CCE that has been occupied by thePDCCH to control section 208.

Control section 208 identifies the A/N resource associated with the CCEon the basis of the information on the CCE received from determinationsection 207.

Control section 208 outputs, to primary-spreading section 214-1, a basesequence and a cyclic shift value corresponding to the A/N resourceassociated with the CCE or the A/N resource previously indicated by basestation 100, and also outputs a Walsh sequence and a DFT sequencecorresponding to the A/N resource to secondary-spreading section 215-1.In addition, control section 208 outputs the frequency resourceinformation on the A/N resource to IFFT section 218-1.

When determining to transmit bundled ACK/NACK signals using a bundledACK/NACK resource, control section 208 outputs the base sequence andcyclic shift value corresponding to the reference signal part (i.e.,reference signal resource) of the bundled ACK/NACK resource previouslyindicated by base station 100 to primary-despreading section 214-2 andoutputs a Walsh sequence to secondary-despreading section 215-2. Inaddition, control section 208 outputs the frequency resource informationon the bundled ACK/NACK resource to IFFT section 218-2.

Control section 208 outputs a DFT sequence used for spreading the datapart of the bundled ACK/NACK resource to spreading section 217 andoutputs the frequency resource information on the bundled ACK/NACKresource to IFFT section 218-3.

Control section 208 selects the bundled ACK/NACK resource or the A/Nresource and instructs selection section 221 to output the selectedresource to radio transmitting section 222. Moreover, control section208 instructs response signal generating section 212 to generate thebundled ACK/NACK signals or the ACK/NACK signals in accordance with theselected resource.

Demodulation section 209 demodulates the downlink data received fromextraction section 204 and outputs the demodulated downlink data (LLR)to decoding section 210.

When the retransmission information received from determination section207 indicates initial transmission, decoding section 210 stores thedownlink data (LLR) received from demodulation section 209 in theretransmission buffer (soft buffer). Decoding section 210 furtherdecodes the downlink data received from demodulation section 209 andoutputs the decoded downlink data to CRC section 211. On the other hand,when the retransmission information received from determination section207 indicates retransmission, decoding section 210 combines the downlinkdata received from demodulation section 209 and the downlink data readfrom the retransmission buffer and stores the combined downlink data inthe retransmission buffer again. Moreover, decoding section 210 decodesthe combined downlink data and outputs the decoded downlink data to CRCsection 211. Details of the method of calculating the retransmissionbuffer size (dividing method) will be described later.

CRC section 211 performs error detection on the decoded downlink datareceived from decoding section 210, for each downlink component carrierusing CRC and outputs an ACK when CRC=OK (no error) or outputs a NACKwhen CRC=Not OK (error) to response signal generating section 212.Moreover, CRC section 211 outputs the decoded downlink data as thereceived data when CRC=OK (no error).

Response signal generating section 212 generates response signals on thebasis of the reception condition of downlink data (i.e., result of errordetection on downlink data) on each downlink component carrier inputtedfrom CRC section 211 and information indicating a predetermined groupnumber. To put it more specifically, when instructed to generate thebundled ACK/NACK signals from control section 208, response signalgenerating section 212 generates the bundled ACK/NACK signals includingthe results of error detection for the respective component carriers asindividual pieces of data. Meanwhile, when instructed to generateACK/NACK signals from control section 208, response signal generatingsection 212 generates ACK/NACK signals of one symbol. Response signalgenerating section 212 outputs the generated response signals to codingand modulation section 213.

Upon reception of the bundled ACK/NACK signals, coding and modulationsection 213 encodes and modulates the received bundled ACK/NACK signalsto generate the modulation signals of 12 symbols and outputs themodulation signals to DFT section 216. In addition, upon reception ofthe ACK/NACK signals of one symbol, coding and modulation section 213modulates the ACK/NACK signals and outputs the modulation signals toprimary-spreading section 214-1.

Primary-spreading sections 214-1 and 214-2 corresponding to the A/Nresources and reference signal resources of the bundled ACK/NACKresources spread the ACK/NACK signals or reference signals using thebase sequence corresponding to the resources in accordance with theinstruction from control section 208 and output the spread signals tosecondary-spreading sections 215-1 and 215-2.

Secondary-spreading sections 215-1 and 215-2 spread the receivedprimary-spread signals using a Walsh sequence or a DFT sequence inaccordance with an instruction from control section 208 and outputs thespread signals to IFFT sections 218-1 and 218-2.

DFT section 216 performs DFT processing on 12 time-series sets ofreceived bundled ACK/NACK signals to obtain 12 signal components in thefrequency-domain. DFT section 216 outputs the 12 signal components tospreading section 217.

Spreading section 217 spreads the 12 signal components received from DFTsection 216 using a DFT sequence indicated by control section 208 andoutputs the spread signal components to IFFT section 218-3.

IFFT sections 218-1, 218-2 and 218-3 perform IFFT processing on thereceived signals in association with the frequency positions where thesignals are to be allocated, in accordance with an instruction fromcontrol section 208. Accordingly, the signals inputted to IFFT sections218-1, 218-2 and 218-3 (i.e., ACK/NACK signals, the reference signals ofA/N resource, the reference signals of bundled ACK/NACK resource andbundled ACK/NACK signals) are transformed into time-domain signals.

CP adding sections 219-1, 219-2 and 219-3 add the same signals as thelast part of the signals obtained by IFFT processing to the beginning ofthe signals as a CP.

Time-multiplexing section 220 time-multiplexes the bundled ACK/NACKsignals received from CP adding section 219-3 (i.e., signals transmittedusing the data part of the bundled ACK/NACK resource) and the referencesignals of the bundled

ACK/NACK resource to be received from CP adding section 219-2 on thebundled ACK/NACK resource and outputs the multiplexed signals toselection section 221.

Selection section 221 selects one of the bundled ACK/NACK resourcereceived from time-multiplexing section 220 and the A/N resourcereceived from CP adding section 219-1 and outputs the signals assignedto the selected resource to radio transmitting section 222.

Radio transmitting section 222 performs transmission processing such asD/A conversion, amplification and up-conversion and/or the like on thesignals received from selection section 221 and transmits the resultantsignals to base station 100 via an antenna.

[Operations of Base Station 100 and Terminal 200]

Operations of base station 100 and terminal 200 having theabove-described configurations will be described.

In the following description, carrier aggregation is applied to terminal200 and terminal 200 communicates with base station 100 using aplurality of component carriers.

A UL-DL configuration (corresponding to a configuration pattern) is setfor each of the plurality of component carriers (PCell and SCell).

Moreover, terminal 200 (radio transmitting section 222) transmitsresponse signals corresponding to downlink data received in PCell amonga plurality of component carriers and response signals corresponding todownlink data received in SCell using PCell. That is, when carrieraggregation is applied, response signals are always transmitted usingPCell. In this case, when the UL-DL configuration set in PCell isdifferent from the UL-DL configuration set in SCell, terminal 200transmits response signals corresponding to downlink data of SCell usingPCell at timings of UL subframes of a reference UL-DL configurationdetermined based on a combination of the UL-DL configurations of PCelland SCell.

Furthermore, terminal 200 supports DL HARQ and maintains aretransmission buffer (soft buffer). When a plurality of componentcarriers (PCell and SCell) are set for terminal 200, the soft bufferincludes a soft buffer for PCell and a soft buffer for SCell.

In the present embodiment, when a set of DL subframes of a UL-DLconfiguration set in PCell is a superset of DL subframes of a UL-DLconfiguration set in SCell (that is, PCell is DL heavy) or when a set ofDL subframes of a UL-DL configuration set in PCell is neither supersetnor subset of DL subframes of a UL-DL configuration set in SCell (thatis, PCell is neither DL heavy nor UL heavy), terminal 200 divides a softbuffer of SCell based on the maximum number of DL HARQ processes definedby a combination of the UL-DL configuration set in PCell and the UL-DLconfiguration set in SCell.

Hereinafter, the maximum number of DL HARQ processes defined by thecombination of the UL-DL configuration set in PCell and the UL-DLconfiguration set in SCell is called “maximum number of DL HARQprocesses to be referenced.” In the present embodiment, the maximumnumber of DL HARQ processes represents a maximum value of the number ofDL HARQ processes to be secured in SCell when SCell references areference UL-DL configuration.

When PCell is DL heavy or PCell is neither DL heavy nor UL heavy, themaximum number of DL HARQ processes to be referenced is set to be equalto or greater than the maximum number of DL HARQ processes defined inthe UL-DL configuration set in SCell and less than the maximum number ofDL HARQ processes defined in the UL-DL configuration (reference UL-DLconfiguration) referenced by SCell for PDSCH-PUCCH timings.

FIGS. 17A to 17C are diagrams provided for describing a method ofsetting the maximum number of DL HARQ processes referenced by SCell.FIG. 17A illustrates a case where Config #0 is set during a non-CAperiod and FIG. 17B illustrates a case where Config #1 is set in PCelland Config #0 is set in SCell (that is, PCell is DL heavy), and FIG. 17Cillustrates a case where Config #1 is set during a non-CA period.Furthermore, in FIG. 17B, SCell references PDSCH-PUCCH timings of Config#1 set in PCell.

For example, in FIG. 17B, the maximum number of DL HARQ processes to bereferenced is set to 5 that satisfies 4 or more, which is the maximumnumber of DL HARQ processes defined in Config #0 (FIG. 17A) set in SCelland less than 7, which is the maximum number of DL HARQ processesdefined in Config #1 (FIG. 17C) referenced by SCell for PDSCH-PUCCHtimings.

Here, when PCell is DL heavy, the range of setting the maximum number ofDL HARQ processes referenced by SCell determined based on thecombination of the UL-DL configuration set in PCell and the UL-DLconfiguration set in SCell will be described.

First, the maximum number of DL HARQ processes referenced by SCell isset to be equal to or greater than the maximum number of DL HARQprocesses defined in the UL-DL configuration set in SCell for thefollowing reason. Namely, this is because in PCell which is DL heavy(that is, PCell whose number of UL subframes is small and which has fewchances of transmitting PUCCH), PDSCH RTT in SCell increases toguarantee PUCCH transmission corresponding to PDSCH of SCell. Forexample, at DL HARQ timing (non-CA) based on Config #0 set in thecomponent carrier shown in FIG. 17A, PDSCH RTT is 10 ms. In contrast,when Config #1 (UL-DL configuration to be referenced) (PDSCH RTT is 11ms) is referenced as PDSCH-PUCCH timing of SCell as shown in FIG. 17B,since a UL-DL configuration which has greater PDSCH RTT and which is DLheavier is referenced, PDSCH RTT is maximum 14 ms, which is greater thanPDSCH RTT of the UL-DL configuration to be referenced. Thus, in FIG. 17Bcompared to FIG. 17A, when PDSCH RTT in SCell increases, the number ofDL HARQ processes to which the IR buffer is to be allocated (that is,the maximum number of DL HARQ processes) increases accordingly. To bemore specific, the maximum number of DL HARQ processes is four in FIG.17A and five in FIG. 17B which is incremented by one. Thus, the maximumnumber of DL HARQ processes referenced by SCell needs to be set to begreater than the maximum number of DL HARQ processes defined in theUL-DL configuration set in SCell.

Here, FIG. 18 illustrates a maximum value of PDSCH RTT in each UL-DLconfiguration. As shown in FIG. 18, PDSCH RTT in Config #1 is 11 msec,whereas PDSCH RTT in Config #6 is 14 msec. When PCell is Config #1 andSCell is Config #6, if PUCCH transmission for PDSCH in SCell isguaranteed in PCell, although the UL-DL configuration to be referenced(Config #1) is DL heavier than the UL-DL configuration (Config #6) setin SCell, PDSCH RTT is smaller. Thus, only in this combination of UL-DLconfigurations, the maximum number of DL HARQ processes referenced bySCell is not necessarily greater than the maximum number of DL HARQprocesses defined in the UL-DL configuration set in SCell. Morespecifically, while Config #1 is DL heavier than Config #6, Config #1has smaller PDSCH RTT, and in a combination when SCell is Config #6(when PCell is DL heavy) in this case, the equality is attained betweenthe maximum number of DL HARQ processes referenced by SCell (that is,the number of divisions of the soft buffer) and the maximum number of DLHARQ processes defined in the UL-DL configuration set in SCell.Furthermore, while Config #2 is DL heavier than Config #6 and hassmaller PDSCH RTT, and in a combination when SCell is Config #6 (whenPCell is DL heavy) in this case, the maximum number of DL HARQ processesreferenced by SCell (that is, the number of divisions of the softbuffer) is greater than the maximum number of DL HARQ processes definedin the UL-DL configuration set in SCell.

Moreover, the maximum number of DL HARQ processes referenced by SCell isset to be less than the maximum number of DL HARQ processes defined inthe UL-DL configuration o be referenced by SCell for the followingreason. Namely, this is because while SCell references the UL-DLconfiguration (Config #1 in FIG. 17B) which is DL heavier than the UL-DLconfiguration (Config #0 in FIG. 17B) set in SCell, the number of DLsubframes assigned to SCell remains that defined in the UL-DLconfiguration (Config #0 in FIG. 17B) set in SCell. That is, since thenumber of DL subframes in the UL-DL configuration set in SCell issmaller than that in the UL-DL configuration to be referenced, thenumber of DL HARQ processes actually required in SCell (maximum numberof DL HARQ processes to be referenced) is smaller than the maximumnumber of DL HARQ processes defined in the UL-DL configuration to bereferenced.

The range of setting the maximum number of DL HARQ processes referencedby SCell when PCell is DL heavy has been described with reference toFIGS. 17A to 17C and FIG. 18, and the same applies to a case where PCellis neither DL heavy nor UL heavy.

FIG. 19A illustrates an example of the maximum number of DL HARQprocesses referenced by SCell determined based on the combination ofUL-DL configurations of PCell and SCell. FIG. 19B illustrates the UL-DLconfiguration referenced by SCell determined based on the combination ofUL-DL configurations of PCell and SCell.

In FIG. 19A, when PCell is UL heavy, the maximum number of DL HARQprocesses referenced by SCell is the same as the maximum number of DLHARQ processes (see FIG. 7B) defined in the UL-DL configuration set inSCell.

On the other hand, in FIG. 19A, when PCell is DL heavy or PCell isneither DL heavy nor UL heavy, it is apparent that the maximum number ofDL HARQ processes to be referenced in both cases is a value equal to orgreater than the maximum number of DL HARQ processes defined in theUL-DL configuration set in SCell and less than the maximum number of DLHARQ processes (see FIG. 7B) defined in the UL-DL configurationreferenced by SCell. In FIG. 19A, a first term of the value indicatingthe maximum number of DL HARQ processes to be referenced indicates themaximum number of DL HARQ processes defined in the UL-DL configurationset in SCell and a second term indicates an increment in the number ofDL HARQ processes caused by the aforementioned increase of PDSCH RTT. Asdescribed above, when PCell is DL heavy as shown in FIG. 19B, the UL-DLconfiguration referenced by SCell is the UL-DL configuration set inPCell. On the other hand, when PCell is neither DL heavy nor UL heavy,the UL-DL configuration referenced by SCell is a UL-DL configuration inwhich DL subframes are set at the same timings as those of both DLsubframes of PCell and SCell.

When the maximum number of DL HARQ processes to be referenced shown inFIG. 19A is defined as M_(REF) _(_) _(DL) _(_) _(HARQ,SCell), IR buffersize N_(IR,SCell) in SCell is expressed by following equation 2. Thatis, the SCell soft buffer is divided into the same number of IR buffersas the maximum number of DL HARQ processes to be referenced M_(REF) _(_)_(DL) _(_) _(HARQ,SCell) or a predetermined threshold M_(limit),whichever is the smaller (where K_(MIMO)=1 is assumed).

[2] $\begin{matrix}{N_{{IR},{SCell}} = \left\lfloor \frac{N_{soft}}{K_{C} \cdot K_{MIMO} \cdot {\min \left( {M_{{{REF}_{—}{DL}_{—}{HARQ}},{SCell}},M_{limit}} \right)}} \right\rfloor} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

On the other hand, as for PCell, the set UL-DL configuration is alwaysthe same as the UL-DL configuration to be referenced.

Therefore, if the maximum number of DL HARQ processes defined in FIG. 7Bis defined as M_(DL) _(_) _(HARQ,PCell), IR buffer size N_(IR,PCell) inPCell is expressed by following equation 3.

[3] $\begin{matrix}{N_{{IR},{PCell}} = \left\lfloor \frac{N_{soft}}{K_{C} \cdot K_{MIMO} \cdot {\min \left( {M_{{{DL}_{—}{HARQ}},{PCell}},M_{limit}} \right)}} \right\rfloor} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

For example, base station 100 and terminal 200 previously store a tablefor determining the maximum number of DL HARQ processes referenced bySCell shown in FIG. 19A. Base station 100 sets respective UL-DLconfigurations of PCell and SCell for terminal 200. Thus, terminal 200identifies the maximum number of DL HARQ processes referenced by SCellbased on a combination of the respective UL-DL configurations of PCelland SCell set for terminal 200 and the table for determining the maximumnumber of DL HARQ processes to be referenced stored therein. Terminal200 then calculates the IR buffer size of SCell (N_(IR,SCell)) and theIR buffer size of PCell (N_(IR,PCell)) according to equation 2 andequation 3.

For example, terminal 200 for which PCell (Config #1) and SCell (Config#0) shown in FIG. 17B are set sets the maximum number of DL HARQprocesses referenced by SCell to 5 with reference to FIG. 19A. Terminal200 then sets M_(REF) _(_) _(DL) _(_) _(HARQ,SCell)=5 and calculates theIR buffer size of SCell (N_(IR,SCell)) according to equation 2.

That is, as shown in FIG. 20, terminal 200 divides the SCell soft bufferbased on the maximum number of DL HARQ processes to be referenced (5processes). In this way, five IR buffers are allocated to SCell.

As described above, according to the present embodiment, terminal 200divides the SCell soft buffer into a plurality of IR buffers (buffersfor the respective retransmission processes) based on a maximum numberof DL HARQ processes to be referenced (corresponding to a specificvalue) determined by a combination of the UL-DL configuration set inPCell and the UL-DL configuration set in SCell.

This allows terminal 200 to allocate SCell IR buffers based on thenumber of DL HARQ processes (that is, maximum number of DL HARQprocesses to be referenced) taking into account the UL-DL configurationreferenced by SCell. By so doing, even when SCell references timings ofa UL-DL configuration to be referenced, it is possible to avoid apossibility that IR buffers may not be successfully allocated to some DLHARQ processes and a coding gain by HARQ retransmission may not beobtained.

That is, according to the present embodiment, terminal 200 can allocateIR buffers to all DL HARQ processes for SCell to thereby support DLHARQ. This allows a coding gain by HARQ to be obtained for all DL HARQprocesses.

According to the present embodiment, when the IR buffers are allocatedas shown in equation 2, the maximum number of DL HARQ processesreferenced by SCell M_(REF) _(_) _(DL) _(_) _(HARQ,SCell) shown in FIG.19A is compared with M_(limit)=8 and whichever is the smaller is usedpreferentially. Thus, base station 100 and terminal 200 may previouslystore a table (e.g., see FIG. 21) for defining the result of calculationof min (M_(REF) _(_) _(DL) _(_) _(HARQ,SCell),M_(limit)) shown inequation 2 in each combination of the UL-DL configuration set in PCelland the UL-DL configuration set in SCell. In terminal 200, thiseliminates the necessity for calculating min (M_(REF) _(_) _(DL) _(_)_(HARQ,SCell),M_(limit)) shown in equation 2.

Furthermore, in the present embodiment, base station 100 and terminal200 may not store any table for determining the maximum number of DLHARQ processes to be referenced shown in FIG. 19A and base station 100may indicate the maximum number of DL HARQ processes referenced by SCellM_(REF) _(_) _(DL) _(_) _(HARQ,SCell) to terminal 200. That is, basestation 100 may indicate the maximum number of DL HARQ processes to bereferenced M_(REF) _(_) _(DL) _(_) _(HARQ,SCell) which is equal to orgreater than the number of DL HARQ processes defined in the UL-DLconfiguration set in SCell and less than the maximum number of DL HARQprocesses defined in the UL-DL configuration referenced by SCell for DLHARQ timings. Alternatively, base station 100 may indicate the result ofcalculation of min (M_(REF) _(_) _(DL) _(_) _(HARQ,SCell),M_(limit))using the maximum number of DL HARQ processes to be referenced toterminal 200.

Embodiment 2

The present embodiment will describe a case where the maximum number ofDL HARQ processes defined in a UL-DL configuration referenced by SCellfor DL HARQ timings is used as the maximum number of DL HARQ processesreferenced by SCell.

In the present embodiment, base station 100 and terminal 200 store atable for determining a UL-DL configuration referenced by SCell shown inFIG. 22A to determine the maximum number of DL HARQ processes referencedby SCell and a table for determining the maximum number of DL HARQprocesses corresponding to each UL-DL configuration shown in FIG. 22B.

To be more specific, terminal 200 identifies a UL-DL configurationreferenced by SCell by referencing the table for determining the UL-DLconfiguration to be referenced shown in FIG. 22A and a combination ofUL-DL configurations respectively set in PCell and SCell. Next, terminal200 identifies the maximum number of DL HARQ processes referenced bySCell M_(REF) _(_) _(DL) _(_) _(HARQ,SCell) by referencing the table fordetermining the maximum number of DL HARQ processes shown in FIG. 22Band the UL-DL configuration referenced by SCell determined using FIG.22A. Terminal 200 then divides an SCell soft buffer based on the maximumnumber of DL HARQ processes to be referenced M_(REF) _(_) _(DL) _(_)_(HARQ,SCell) according to equation 2 as in the case of Embodiment 1.

For example, when Config #1 is set in PCell and Config #0 is set inSCell for terminal 200, terminal 200 determines Config #1 as the UL-DLconfiguration referenced by SCell with reference to the table shown inFIG. 22A. Next, terminal 200 determines the maximum number of DL HARQprocesses referenced by SCell M_(REF) _(_) _(DL) _(_) _(HARQ,SCell)=7with reference to determined Config #1 and the table shown in FIG. 22B.In this case, terminal 200 divides the SCell soft buffer into seven IRbuffers.

In FIG. 22A, when PCell is DL heavy, the UL-DL configuration referencedby SCell is a UL-DL configuration set in PCell and when PCell is ULheavy (that is, SCell is DL heavy), the UL-DL configuration referencedby SCell is a UL-DL configuration set in SCell, and when PCell isneither DL heavy nor UL heavy, the UL-DL configuration referenced bySCell is a UL-DL configuration which is DL heavy with respect to bothPCell and SCell.

That is, the same or a DL heavy UL-DL configuration with respect to theUL-DL configuration set in SCell is always set as the UL-DLconfiguration referenced by SCell.

The DL heavier the UL-DL configuration, the greater the number of DLHARQ processes that is required. However, as described in Embodiment 1,when SCell references DL HARQ timings of the UL-DL configuration to bereferenced, the number of DL HARQ processes necessary for SCell neverexceeds the maximum number of DL HARQ processes defined in the UL-DLconfiguration referenced by SCell.

Thus, as in the case of the present embodiment, using the maximum numberof DL HARQ processes defined in the UL-DL configuration referenced bySCell as the maximum number of DL HARQ processes referenced by SCellused to determine the number of divisions of the SCell soft buffer,terminal 200 can allocate the IR buffers to all DL HARQ processes forSCell to thereby support DL HARQ. Thus, according to the presentembodiment, it is possible to obtain a coding gain by HARQ for all DLHARQ processes.

FIG. 22B is the same table as the existing table shown in FIG. 7B.Moreover, FIG. 22A is the same table as that in FIG. 19B. The tableshown in FIG. 22A (FIG. 19B) is a table necessary to define DL HARQtimings of SCell (that is, transmission timing of response signals ofSCell transmitted using PCell) as described above. That is, the tableshown in FIG. 22A is a necessary table regardless of the determinationof the number of divisions of the SCell soft buffer. That is, in thepresent embodiment, base station 100 and terminal 200 need not store newtables (e.g., the table shown in FIG. 19A) to determine the number ofdivisions of the SCell soft buffer. According to the present embodiment,it is thereby possible to make the configurations of base station 100and terminal 200 simpler than those in Embodiment 1.

Embodiment 3

Embodiment 1 has described instances when cross-carrier scheduling isnot set (which may also be referred to as “when CIF (cross indicatorfield) is not set” or “when self-scheduling is set”). That is, a casehas been described in Embodiment 1 where DL assignment of PCell to PDSCH(resource assignment information) is indicated by PDCCH of PCell and DLassignment of SCell to PDSCH is indicated by PDCCH of SCell.

In contrast, the present embodiment will describe a case where across-carrier scheduling setting is taken into account.

Cross-carrier scheduling is a technique that uses PDCCH of a certaincomponent carrier to schedule resource assignment of another componentcarrier. For example, in preparation for a case where when quality ofPDCCH in SCell cannot be guaranteed in such a case as when terminal 200receives large interference regarding DL assignment (resource assignmentinformation) of SCell to PDSCH, cross-carrier scheduling from PCell toSCell is performed. In this case, base station 100 indicates DLassignment of SCell to PDSCH using PDCCH of PCell (e.g., dotted linearrows shown in FIGS. 23A and 23B).

When cross-carrier scheduling is set and when PCell is UL heavy (seeFIG. 23A) or when PCell is neither DL heavy nor UL heavy (not shown),there are timings at which PCell becomes a UL subframe and SCell becomesa DL subframe (e.g., SF #4 and #9 shown in FIG. 23A). At these timings,base station 100 cannot indicate DL assignment indicating PDSCH of SCellusing PDCCH of PCell, and therefore it is not possible to assign PDSCHof SCell. Therefore, DL subframes of SCell cannot be used at thetimings.

On the other hand, when cross-carrier scheduling is not set (not shown),DL assignment indicating PDSCH of SCell is indicated using PDCCH ofSCell, and therefore DL subframes can be used in SCell even at timingsat which PCell becomes a UL subframe and SCell becomes a DL subframe.

Thus, whether or not it is possible to use DL subframes of SCell attimings at which PCell becomes a UL subframe and SCell becomes a DLsubframe is one of differences when cross-carrier scheduling is not setand when cross-carrier scheduling is set in a case where a UL-DLconfiguration varies among a plurality of component carriers.

Since DL subframes of SCell cannot be used at the above-describedtimings, the number of DL subframes usable in SCell is smaller whencross-carrier scheduling is set than when cross-carrier scheduling isnot set. For this reason, the maximum number of DL HARQ processesreferenced by SCell is also smaller when cross-carrier scheduling is setthan when cross-carrier scheduling is not set. Thus, the number ofdivisions of the SCell soft buffer determined based on the maximumnumber of DL HARQ processes referenced by SCell is smaller whencross-carrier scheduling is set than when cross-carrier scheduling isnot set.

Note that in FIG. 23A, at timings at which PCell becomes a UL subframeand SCell becomes a DL subframe (SF #4, #9), neither DL subframes ofSCell nor UL subframes (SF #8, #3) of PCell corresponding to the DLsubframes at PDSCH-PUCCH timings can be used. For this reason, whencross-carrier scheduling is set and when PCell is UL heavy, it ispreferable for SCell to always reference PDSCH-PUCCH timings of a UL-DLconfiguration set in PCell as shown in FIG. 23B. This makes it possibleto avoid a possibility that UL subframes of PCell corresponding to DLsubframes of SCell at PDSCH-PUCCH timings may not be used.

By the way, whether or not to set cross-carrier scheduling is changedbased on indication of RRC (radio resource control) from base station100. Moreover, as described above, the number of divisions of the SCellsoft buffer and the number of DL HARQ processes vary when cross-carrierscheduling is set and when cross-carrier scheduling is not set.Therefore, when base station 100 changes the setting of cross-carrierscheduling, as shown in FIG. 24, the number of divisions of the SCellsoft buffer is changed before and after the setting change and thereference position of data stored in the soft buffer changes.

For this reason, there is a problem that DL HARQ of SCell cannot becontinued before and after the setting of cross-carrier scheduling ischanged.

Thus, in the present embodiment, terminal 200 divides the SCell softbuffer based on the maximum number of DL HARQ processes to be referencedwhen cross-carrier scheduling is set or when cross-carrier scheduling isnot set (that is, when self-scheduling is set), whichever is thegreater. That is, the number of divisions of the soft buffer isdetermined based on not the situation as to whether or not cross-carrierscheduling is set, but the maximum number of DL HARQ processes to bereferenced when either one scheduling method is set.

More specifically, as described above, the maximum number of DL HARQprocesses to be referenced is greater when cross-carrier scheduling isnot set than when cross-carrier scheduling is set. Thus, terminal 200divides the SCell soft buffer not based on the situation as to whetheror not cross-carrier scheduling is set, but always based on the maximumnumber of DL HARQ processes to be referenced when cross-carrierscheduling is not set. For example, terminal 200 may also determine themaximum number of DL HARQ processes to be referenced when cross-carrierscheduling is not set with reference to the table shown in FIG. 19A asin the case of Embodiment 1. Alternatively, terminal 200 may determinethe maximum number of DL HARQ processes to be referenced whencross-carrier scheduling is not set with reference to the table shown inFIG. 22A and FIG. 22B as in the case of Embodiment 2.

By so doing, when cross-carrier scheduling is not set, it is possible toallocate IR buffers to all DL HARQ processes and support DL HARQ as inthe case of Embodiment 1 or 2. Moreover, when cross-carrier schedulingis set with a smaller number of necessary DL HARQ processes than whencross-carrier scheduling is not set, it is possible to allocate IRbuffers to all DL HARQ processes and support DL HARQ. Therefore,according to the present embodiment, it is possible to allocate IRbuffers to all DL HARQ processes and support DL HARQ before and afterchanging the setting of cross-carrier scheduling.

Furthermore, according to the present embodiment, the method of dividingthe SCell soft buffer is not changed before and after changing thesetting of cross-carrier scheduling. Thus, the reference position ofdata stored in the soft buffer is not changed before and after changingthe setting of cross-carrier scheduling, and it is thereby possible tocontinue DL HARQ processes of SCell. Thus, it is possible to obtain acoding gain by HARQ for all DL HARQ processes.

When the setting of cross-carrier scheduling is less frequently changed,the coding gain associated with the fact of being able to continue DLHARQ before and after changing the setting of cross-carrier schedulingis reduced. That is, when the setting of cross-carrier scheduling isless frequently changed, the influence of the fact of not being able tocontinue DL HARQ is small. Thus, when the setting of cross-carrierscheduling is less frequently changed, base station 100 and terminal 200may determine the maximum number of DL HARQ processes referenced bySCell with reference to the table shown in FIG. 25 when cross-carrierscheduling is set or determine the maximum number of DL HARQ processesreferenced by SCell with reference to the table in Embodiment 1 (FIG.19A) or the table in Embodiment 2 (FIG. 22A and FIG. 22B) whencross-carrier scheduling is not set. In FIG. 25, when PCell is UL heavy,the maximum number of DL HARQ processes defined in the UL-DLconfiguration set in PCell is set as the maximum number of DL HARQprocesses to be referenced. Moreover, in FIG. 25, when PCell is DL heavyor PCell is neither DL heavy nor UL heavy, a value obtained bysubtracting from the maximum number of DL HARQ processes (first term)defined in the UL-DL configuration set in PCell, the decrement (secondterm) in the number of DL HARQ processes caused by a reduction in thenumber of DL subframes that cannot be used from the UL-DL configurationset in PCell due to the fact that DL subframes cannot be used at timingsat which PCell becomes a DL subframe and SCell becomes a UL subframe, isset as the maximum number of DL HARQ processes to be referenced.

Embodiment 4

The present embodiment will describe a case where a UL-DL configurationof each component carrier is dynamically changed (that is, when TDDeIMTA is applied).

As an example of application of TDD eIMTA, a UL-DL configuration may bedynamically changed in a pico cell (SCell) in inter-band carrieraggregation between a macro cell (Pcell) and a pico cell (SCell).

When different UL-DL configurations are set between terminals supportingTDD eIMTA, interference from uplink communication to downlinkcommunication (hereinafter may be referred to as “UL-DL interference”)may occur between the terminals. To avoid the occurrence of this UL-DLinterference, terminals supporting TDD eIMTA may change the UL-DLconfiguration not for each terminal (UE specific) but for each cell(cell specific).

When the UL-DL configuration is changed for each cell, many terminalssupporting TDD eIMTA are likely to change the UL-DL configuration whileall DL HARQ processes have not been completed (that is, no ACK has beenreturned to the base station).

Furthermore, as shown in FIG. 7B, the maximum number of DL HARQprocesses (M_(DL) _(_) _(HARQ)) varies among different UL-DLconfigurations. For this reason, when the maximum number of DL HARQprocesses corresponding to any one UL-DL configuration at least beforeand after the change is less than 8, the IR buffer size per TB alsovaries before and after the change of the UL-DL configuration. Forexample, in FIG. 26, when Config #0 is changed to Config #1, the maximumnumber of DL HARQ processes is also changed from 4 to 7.

Thus, as shown in FIG. 26, since the number of divisions of the softbuffer also varies before and after the change of the UL-DLconfiguration, the data reference position in the soft buffer variesbefore and after the change of the UL-DL configuration. For this reasonthe terminal cannot correctly read the stored data and cannot continueDL HARQ before and after the change of the UL-DL configuration, andtherefore there is concern about deterioration of HARQ retransmissionperformance before and after the change of the UL-DL configuration.Although the deterioration of HARQ retransmission performance isobserved in aforementioned method (1) of changing the UL-DLconfiguration or in the case of a change of the UL-DL configuration witha low or medium frequency as shown in method (2), such deterioration ofHARQ retransmission performance appears more noticeably particularlywhen the UL-DL configuration is changed with a high frequency as shownin method (3).

Thus, in the present embodiment, when different UL-DL configurations areset between component carriers and when a UL-DL configuration isdynamically changed in each cell, base station 100 limits a combinationof UL-DL configurations of PCell and SCell that can be set for terminal200 and divides the SCell soft buffer using a maximum value of themaximum number of DL HARQ processes to be referenced defined in thecombination of UL-DL configurations. That is, terminal 200 divides theSCell soft buffer based on a maximum value of the maximum number of DLHARQ processes to be referenced respectively determined by candidategroups of combinations of UL-DL configurations of PCell and SCell thatcan be set for terminal 200.

FIG. 27A illustrates an example of the method of setting the maximumnumber of DL HARQ processes referenced by SCell according to the presentembodiment. FIG. 27B illustrates an example of the UL-DL configurationreferenced by SCell according to the present embodiment.

In the following description, among the combinations of UL-DLconfigurations of PCell and SCell shown in FIG. 27A, combinations(PCell, SCell) that can be set for terminal 200 are assumed to be thefollowing six sets: (Config #0, Config #0), (Config #0, Config #6),(Config #0, Config #1), (Config #6, Config #6), (Config #6, Config #1)and (Config #1, Config #1) (combinations enclosed by ellipses).

As shown in FIG. 27A, the maximum number of DL HARQ processes referencedby SCell are 4, 6, 7, 6, 7, 7 respectively in order of combinations(PCell, SCell) of PCell and SCell that can be set for terminal 200above. Terminal 200 divides the SCell soft buffer using the maximumvalue 7 among these maximum numbers of DL HARQ processes to bereferenced. For example, assuming M_(REF) _(_) _(DL) _(_)_(HARQ,SCell)=7 in equation 2, terminal 200 calculates IR buffers forSCell. In this case, terminal 200 divides the SCell soft buffer intoseven IR buffers.

By so doing, even when the combination of PCell and SCell is changed toany combination that can be set for terminal 200, terminal 200 willnever run short of SCell IR buffers. Thus, according to the presentembodiment, terminal 200 can obtain a coding gain by HARQ for all DLHARQ processes corresponding to SCell.

Since the number of divisions of the SCell soft buffer is not changedbefore and after the change of the UL-DL configuration, data referencepositions on the soft buffer are not changed either. Thus, even when theUL-DL configuration is changed, terminal 200 can correctly read the datastored before the change, and can thereby continue DL HARQ before andafter the change of the UL-DL configuration. According to the presentembodiment, it is possible to avoid deterioration of HARQ retransmissionperformance before and after the change of the UL-DL configuration.

Base station 100 may previously indicate combinations of UL-DLconfigurations of PCell and SCell that can be set for terminal 200.Alternatively, instead of indicating combinations of UL-DLconfigurations of PCell and SCell that can be set for terminal 200, basestation 100 may indicate the result of calculation of min (M_(REF) _(_)_(DL) _(_) _(HARQ,SCell),M_(limit)) to terminal 200. In this case, sincethe calculation result takes values 4 to 8, the result can be indicatedusing 3 bits. On the other hand, since there are seven UL-DLconfigurations of Config #0 to #6 (3 bits) to indicate combinations ofUL-DL configurations of PCell and SCell, (3+3)×n (n: number ofcombinations) bits are required. Base station 100 indicates only theabove calculation result, and it is thereby possible to drasticallyreduce the number of bits to be indicated to terminal 200 compared tothe case where combinations of UL-DL configurations of PCell and SCellare indicated.

In FIG. 27A, there are 34 out of total 49 sets of combinations in whichthe maximum number of DL HARQ processes referenced by SCell becomes 8 ormore, which is a large number. Therefore, the calculation result of min(M_(REF) _(_) _(DL) _(_) _(HARQ,SCell),M_(limit)) in equation 2 islikely to be 8 (=M_(limit)) in many combinations. Thus, base station 100may not previously indicate the combinations of UL-DL configurations ofPCell and SCell that can be set for terminal 200 or the calculationresult of min (M_(REF) _(_) _(DL) _(_) _(HARQ,SCell),M_(limit)) toterminal 200, and terminal 200 may perform the following operation.

To be more specific, when different UL-DL configurations are set betweencomponent carriers and UL-DL configurations are set to be dynamicallychanged (when TDD eIMTA is set), terminal 200 may calculate the IRbuffer size of SCell by always assuming min (M_(REF) _(_) _(DL) _(_)_(HARQ,SCell),M_(limit)=8. On the other hand, when different UL-DLconfigurations are set between component carriers and UL-DLconfigurations are not set to be dynamically changed (when TDD eIMTA isnot set), terminal 200 may calculate the IR buffer size of SCellaccording to the methods shown in Embodiments 1 to 3.

A case where cross-carrier scheduling is set may also be studied in thepresent embodiment as in the case of Embodiment 3. That is, terminal 200may divide the SCell soft buffer into equal portions using a maximumvalue between the maximum number of DL HARQ processes to be referencedwhen cross-carrier scheduling is not set which is defined bycombinations of UL-DL configurations of PCell and SCell that can be setfor terminal 200 and the maximum number of DL HARQ processes to bereferenced when cross-carrier scheduling is set.

More specifically, as described in Embodiment 3, the maximum number ofDL HARQ processes to be referenced is greater when cross-carrierscheduling is not set than when cross-carrier scheduling is set. Thus,terminal 200 may divide the SCell soft buffer always using a maximumvalue among the maximum numbers of DL HARQ processes to be referencedwhen cross-carrier scheduling is not set which is defined bycombinations of UL-DL configurations that can be set for terminal 200irrespective of whether or not cross-carrier scheduling is set.

The embodiments of the present invention have been described so far.

The expression “SCell” has been used in the embodiments of the presentinvention, but SCell is not limited to one SCell or SCell for which onetype of UL-DL configuration is set. That is, this is applicable to PCelland each SCell respectively. Furthermore, different UL-DL configurationsmay be set to respective SCells.

Although an antenna has been described in the aforementionedembodiments, the present invention may be similarly applied to anantenna port.

The term “antenna port” refers to a logical antenna including one ormore physical antennas. In other words, the term “antenna port” does notnecessarily refer to a single physical antenna, and may sometimes referto an antenna array including a plurality of antennas, and/or the like.

For example, how many physical antennas are included in the antenna portis not defined in LTE, but the antenna port is defined as the minimumunit allowing the base station to transmit different reference signalsin LTE.

In addition, an antenna port may be specified as a minimum unit to bemultiplied by a precoding vector weighting.

In the foregoing embodiments, the present invention is configured withhardware by way of example, but the invention may also be provided bysoftware in cooperation with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

A terminal apparatus according to the embodiments described above is anapparatus which communicates with a base station apparatus using aplurality of component carriers and for which a configuration pattern ofsubframes included in one frame is set for each of the plurality ofcomponent carriers, the configuration pattern including a downlinkcommunication subframe used for downlink communication and an uplinkcommunication subframe used for uplink communication, the terminalapparatus including: a decoding section that stores, in a retransmissionbuffer, downlink data transmitted in each of the plurality of componentcarriers and decodes the downlink data; a generating section thatgenerates a response signal using a result of error detection of thedownlink data; and a transmitting section that transmits, using a firstcomponent carrier of the plurality of component carriers, a responsesignal for first downlink data received using the first componentcarrier and a response signal for second downlink data received using asecond component carrier of the plurality of component carriers, inwhich: the buffer includes a first buffer that stores the first downlinkdata and a second buffer that stores the second downlink data; and thesecond buffer is divided into regions respectively corresponding toretransmission processes based on a specific value determined by acombination of a first configuration pattern that is set in the firstcomponent carrier and a second configuration pattern that is set in thesecond component carrier.

In the terminal apparatus according to the embodiments described above:when the first configuration pattern and the second configurationpattern are different, the transmitting section transmits a responsesignal for the second downlink data using the first component carrier ata timing of an uplink communication subframe of a third configurationpattern to be determined based on the combination; and the specificvalue is a maximum value of a number of retransmission processes definedin the third configuration pattern.

In the terminal apparatus according to the embodiments described above:in the combination including the first configuration pattern in which adownlink communication subframe is set at least at a timing identical toa timing of a downlink communication subframe of the secondconfiguration pattern, the third configuration pattern is the firstconfiguration pattern; in the combination in which the firstconfiguration pattern and the second configuration pattern respectivelyinclude downlink communication subframes that are set at least atdifferent timings, the third configuration pattern is a fourthconfiguration pattern in which downlink communication subframes are setat least at timings identical to the timings of both downlinkcommunication subframes of the first configuration pattern and thesecond configuration pattern; and in the combination including thesecond configuration pattern in which a downlink communication subframeis set at least at a timing identical to a timing of downlinkcommunication subframe of the first configuration pattern, the thirdconfiguration pattern is the second configuration pattern.

In the terminal apparatus according to the embodiments described above:when the first configuration pattern and the second configurationpattern are different, the transmitting section transmits a responsesignal for the second downlink data using the first component carrier ata timing of an uplink communication subframe of a third configurationpattern to be determined based on the combination; in a firstcombination including the first configuration pattern in which adownlink communication subframe that is set at least at a timingidentical to a timing of a downlink communication subframe of the secondconfiguration pattern, or in a second combination in which the firstconfiguration pattern and the second configuration pattern respectivelyinclude downlink communication subframes that are set at least atdifferent timings, the specific value is a value equal to or greaterthan a maximum value of a number of retransmission processes defined inthe second configuration pattern but less than a maximum value of anumber of retransmission processes defined in the third configurationpattern; and in a third combination including the second configurationpattern in which a downlink communication subframe that is set at leastat a timing identical to a timing of a downlink communication subframeof the first configuration pattern, the specific value is a maximumvalue of a number of retransmission processes defined in the secondconfiguration pattern.

In the terminal apparatus according to the embodiments described above:in the first combination, the third configuration pattern is the firstconfiguration pattern; in the second combination, the thirdconfiguration pattern is a fourth configuration pattern in whichdownlink communication subframes are set at least at timings identicalto the timings of both downlink communication subframes of the firstconfiguration pattern and the second configuration pattern; and in thethird combination, the third configuration pattern is the secondconfiguration pattern.

In the terminal apparatus according to the embodiments described above:a scheduling method for the terminal apparatus is switchable between afirst scheduling method that indicates resource assignment informationon the first downlink data using the first component carrier and thatindicates resource assignment information on the second downlink datausing the second component carrier, and a second scheduling method thatindicates resource assignment information on both the first downlinkdata and the second downlink data using the first component carrier; andthe second buffer is divided based on the specific value when the firstscheduling method is set.

In the terminal apparatus according to the embodiments described above,the specific value is a maximum value among values respectivelydetermined from candidate groups of the combinations allowed to be setfor the terminal apparatus.

In the terminal apparatus according to the embodiments described above,the second buffer is divided into a number of regions that is identicalto a smaller one of the specific value and a predetermined threshold.

In the terminal apparatus according to the embodiments described above,the first component carrier is a primary cell and the second componentcarrier is a secondary cell.

A buffer dividing method according to the embodiments described above isa method for a terminal apparatus which communicates with a base stationapparatus, using a plurality of component carriers and in which aconfiguration pattern of subframes included in one frame is set for eachof the plurality of component carriers, the configuration patternincluding a downlink communication subframe used for downlinkcommunication and an uplink communication subframe used for uplinkcommunication, the method including: storing, in a retransmissionbuffer, downlink data transmitted in each of the plurality of componentcarriers; decoding the downlink data; generating a response signal usinga result of error detection of the downlink data; and transmitting,using a first component carrier of the plurality of component carriers,a response signal for first downlink data received in the firstcomponent carrier and a response signal for second downlink datareceived in a second component carrier of the plurality of componentcarriers, in which: the buffer includes a first buffer that stores thefirst downlink data and a second buffer that stores the second downlinkdata; and the second buffer is divided into regions respectivelycorresponding to retransmission processes based on a specific valuedetermined by a combination of a first configuration pattern that is setin the first component carrier and a second configuration pattern thatis set in the second component carrier.

The disclosure of Japanese Patent Application No. 2012-158677, filed onJul. 17, 2012, including the specification, drawings and abstract isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in mobile communicationsystems, for example.

REFERENCE SIGNS LIST

-   -   100 Base station    -   200 Terminal    -   101, 208 Control section    -   102 Control information generating section    -   103, 105 Coding section    -   104, 107 Modulation section    -   106 Data transmission controlling section    -   108 Mapping section    -   109, 218 IFFT section    -   110, 219 CP adding section    -   111, 222 Radio transmitting section    -   112, 201 Radio receiving section    -   113, 202 CP removing section    -   114 PUCCH extracting section    -   115 Despreading section    -   116 Sequence controlling section    -   117 Correlation processing section    -   118 A/N determining section    -   119 Bundled A/N despreading section    -   120 IDFT section    -   121 Bundled A/N determining section    -   122 Retransmission control signal generating section    -   203 FFT section    -   204 Extraction section    -   205, 209 Demodulation section    -   206, 210 Decoding section    -   207 Determination section    -   211 CRC section    -   212 Response signal generating section    -   213 Coding and modulation section    -   214 Primary-spreading section    -   215 Secondary-spreading section    -   216 DFT section    -   217 Spreading section    -   220 Time multiplexing section    -   221 Selection section

1. An integrated circuit, which, in operation, controls a processperformed at a base station configured to communicate with a terminal,the process comprising: transmitting and retransmitting first and seconddownlink data in first and second component carriers, respectively,wherein a first configuration pattern of UL (uplink) and DL (downlink)subframes is set for the first component carrier and a secondconfiguration pattern of UL and DL subframes is set for the secondcomponent carrier; and receiving from the terminal in the firstcomponent carrier an ACK/NACK (acknowledgement/negative acknowledgement)for the first and second downlink data received by the terminal, whichstores retransmission data of the first and second downlink data in asoft buffer, wherein the soft buffer for the second downlink data issized according to a maximum number of downlink HARQ (hybrid automaticrepeat request) retransmission processes executable in a referenceconfiguration pattern of UL and DL subframes, the maximum number ofdownlink HARQ retransmission processes is determined according to thereference configuration pattern, and the reference configuration patternis determined according to the first and second configuration patterns.2. The integrated circuit according to claim 1, wherein the receivingstep includes receiving the ACK/NACK at a timing of an UL subframe ofthe reference configuration pattern.
 3. The integrated circuit accordingto claim 1, wherein, when the first configuration pattern and the secondconfiguration pattern are different, the receiving step includesreceiving the ACK/NACK at a timing of an UL subframe of the referenceconfiguration pattern.
 4. The integrated circuit according to claim 1,wherein the first component carrier is a primary cell (PCell) and thesecond component carrier is a secondary cell (SCell).
 5. The integratedcircuit according to claim 4, wherein when a set of DL subframes ofPCell included in one frame includes a set of DL subframes of SCell, thereference configuration pattern is the same as the first configurationpattern.
 6. The integrated circuit according to claim 4, wherein when aset of DL subframes of SCell included in one frame includes a set of DLsubframes of PCell, the reference configuration pattern is the same asthe second configuration pattern.
 7. The integrated circuit according toclaim 4, wherein when a set of DL subframes of SCell is not included ina set of DL subframes of PCell included in one frame and the set of DLsubframes of PCell is not included in the set of DL subframes of SCell,the reference configuration pattern is a UL-DL configuration patternwhich is DL heavy with respect to both PCell and SCell.
 8. Theintegrated circuit according to claim 1, wherein the soft buffer storesan LLR (Log Likelihood Ratio) of the second downlink data when error isdetected by the terminal, to be combined with an LLR of the seconddownlink data that is retransmitted.
 9. An integrated circuit, which, inoperation, controls a process performed at a base station configured tocommunicate with a terminal, the integrated circuit comprising:transmission circuitry configured to transmit and retransmit first andsecond downlink data in first and second component carriers,respectively, wherein a first configuration pattern of UL (uplink) andDL (downlink) subframes is set for the first component carrier and asecond configuration pattern of UL and DL subframes is set for thesecond component carrier; and reception circuitry configured to receivefrom the terminal in the first component carrier an ACK/NACK(acknowledgement/negative acknowledgement) for the first and seconddownlink data received by the terminal, which stores retransmission dataof the first and second downlink data in a soft buffer, wherein the softbuffer for the second downlink data is sized according to a maximumnumber of downlink HARQ (hybrid automatic repeat request) retransmissionprocesses executable in a reference configuration pattern of UL and DLsubframes, the maximum number of downlink HARQ retransmission processesis determined according to the reference configuration pattern, and thereference configuration pattern is determined according to the first andsecond configuration patterns.
 10. The integrated circuit according toclaim 9, wherein the reception circuitry receives the ACK/NACK at atiming of an UL subframe of the reference configuration pattern.
 11. Theintegrated circuit according to claim 9, wherein, when the firstconfiguration pattern and the second configuration pattern aredifferent, the reception circuitry receives the ACK/NACK at a timing ofan UL subframe of the reference configuration pattern.
 12. Theintegrated circuit according to claim 9, wherein the first componentcarrier is a primary cell (PCell) and the second component carrier is asecondary cell (SCell).
 13. The integrated circuit according to claim12, wherein when a set of DL subframes of PCell included in one frameincludes a set of DL subframes of SCell, the reference configurationpattern is the same as the first configuration pattern.
 14. Theintegrated circuit according to claim 12, wherein when a set of DLsubframes of SCell included in one frame includes a set of DL subframesof PCell, the reference configuration pattern is the same as the secondconfiguration pattern.
 15. The integrated circuit according to claim 12,wherein when a set of DL subframes of SCell is not included in a set ofDL subframes of PCell included in one frame and the set of DL subframesof PCell is not included in the set of DL subframes of SCell, thereference configuration pattern is a UL-DL configuration pattern whichis DL heavy with respect to both PCell and SCell.
 16. The integratedcircuit according to claim 9, wherein the soft buffer stores an LLR (LogLikelihood Ratio) of the second downlink data when error is detected bythe terminal, to be combined with an LLR of the second downlink datathat is retransmitted.